A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows small electronic receivers to determine their location (longitude, latitude, and altitude/elevation) to high precision (within a few metres) using time signals transmitted along a line of sight by radio from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking), the signals also allow the electronic receiver to calculate the current local time to high precision, which allows time synchronisation. Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.

GNSS-2[citation needed] is the second generation of systems that independently provides a full civilian satellite navigation system, exemplified by the European Galileo positioning system. These systems will provide the accuracy and integrity monitoring necessary for civil navigation; including aircraft. This system consists of L1 and L2 frequencies (in the L band of the radio spectrum) for civil use and L5 for system integrity. Development is also in progress to provide GPS with civil use L2 and L5 frequencies, making it a GNSS-2 system.¹[citation needed]

Continental scale Ground Based Augmentation Systems (GBAS) for example the Australian GRAS and the joint US Coast Guard, Canadian Coast Guard, US Army Corps of Engineers and US Department of Transportation National Differential GPS (DGPS) service.

Regional scale GBAS such as CORS networks.

Local GBAS typified by a single GPS reference station operating Real Time Kinematic (RTK) corrections.

Ground based radio navigation has long been practiced, the DECCA, LORAN, GEE and Omega systems used terrestrial longwave radio transmitters which broadcast a radio pulse from a known "master" location, followed by a pulse repeated from a number of "slave" stations. The delay between the reception of the master signal and the slave signals allowed the receiver to deduce the distance to each of the slaves, providing a fix.

The first satellite navigation system was Transit, a system deployed by the US military in the 1960s. Transit's operation was based on the Doppler effect: the satellites travelled on well-known paths and broadcast their signals on a well-known radio frequency, the received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position.

Part of an orbiting satellite's broadcast included its precise orbital data; in order to ensure accuracy, the US Naval Observatory (USNO) continuously observed the precise orbits of these satellites. As a satellite's orbit deviated, the USNO would send the updated information to the satellite. Subsequent broadcasts from an updated satellite would contain its most recent ephemeris.

Modern systems are more direct, the satellite broadcasts a signal that contains orbital data (from which the position of the satellite can be calculated) and the precise time the signal was transmitted. The orbital ephemeris is transmitted in a data message that is superimposed on a code that serves as a timing reference, the satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. The receiver compares the time of broadcast encoded in the transmission of three (at sea level) or four different satellites, thereby measuring the time-of-flight to each satellite. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time using an adapted version of trilateration: see GNSS positioning calculation for details.

Each distance measurement, regardless of the system being used, places the receiver on a spherical shell at the measured distance from the broadcaster. By taking several such measurements and then looking for a point where they meet, a fix is generated. However, in the case of fast-moving receivers, the position of the signal moves as signals are received from several satellites; in addition, the radio signals slow slightly as they pass through the ionosphere, and this slowing varies with the receiver's angle to the satellite, because that changes the distance through the ionosphere. The basic computation thus attempts to find the shortest directed line tangent to four oblate spherical shells centred on four satellites. Satellite navigation receivers reduce errors by using combinations of signals from multiple satellites and multiple correlators, and then using techniques such as Kalman filtering to combine the noisy, partial, and constantly changing data into a single estimate for position, time, and velocity.

The original motivation for satellite navigation was for military applications. Satellite navigation allows precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from mis-directed weapons. (See Guided bomb). Satellite navigation also allows forces to be directed and to locate themselves more easily, reducing the fog of war.

The ability to supply satellite navigation signals is also the ability to deny their availability, the operator of a satellite navigation system potentially has the ability to degrade or eliminate satellite navigation services over any territory it desires.

The United States' Global Positioning System (GPS) consists of up to 32 medium Earth orbit satellites in six different orbital planes, with the exact number of satellites varying as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is currently the world's most utilized satellite navigation system.

The formerly Soviet, and now Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema (Russian: ГЛОбальная НАвигационная Спутниковая Система, GLObal NAvigation Satellite System), or GLONASS, is a space-based satellite navigation system that provides a civilian radionavigation-satellite service and is also used by the Russian Aerospace Defence Forces. The full orbital constellation of 24 GLONASS satellites enables full global coverage.

The European Union and European Space Agency agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system. Galileo became operational on 15 December 2016 (global Early Operational Capability (EOC)) [4] At an estimated cost of EUR 3.0 billion,[5] the system of 30 MEO satellites was originally scheduled to be operational in 2010. The original year to become operational was 2014,[6] the first experimental satellite was launched on 28 December 2005.[7] Galileo is expected to be compatible with the modernized GPS system, the receivers will be able to combine the signals from both Galileo and GPS satellites to greatly increase the accuracy. Galileo is expected to be in full service in 2020 and at a substantially higher cost,[1] the main modulation used in Galileo Open Service signal is the Composite Binary Offset Carrier (CBOC) modulation.

China has indicated they plan to complete the entire second generation Beidou Navigation Satellite System (BDS or BeiDou-2, formerly known as COMPASS), by expanding current regional (Asia-Pacific) service into global coverage by 2020.[2] The BeiDou-2 system is proposed to consist of 30 MEO satellites and five geostationary satellites. A 16-satellite regional version (covering Asia and Pacific area) was completed by December 2012.

The NAVIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by Indian Space Research Organisation (ISRO) which would be under the total control of Indian government. The government approved the project in May 2006, with the intention of the system completed and implemented on 28 April 2016, it will consist of a constellation of 7 navigational satellites.[8] 3 of the satellites will be placed in the Geostationary orbit (GEO) and the remaining 4 in the Geosynchronous orbit(GSO) to have a larger signal footprint and lower number of satellites to map the region. It is intended to provide an all-weather absolute position accuracy of better than 7.6 meters throughout India and within a region extending approximately 1,500 km around it.[9] A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India.[10] All seven satellites, IRNSS-1A, IRNSS-1B, IRNSS-1C, IRNSS-1D, IRNSS-1E, IRNSS-1F, and IRNSS-1G, of the proposed constellation were precisely launched on 1 July 2013, 4 April 2014, 16 October 2014, 28 March 2015, 20 January 2016, 10 March 2016 and 28 April 2016 respectively from Satish Dhawan Space Centre.[11][12] The system is expected to be fully operational by August 2016.[13]

The Quasi-Zenith Satellite System (QZSS), is a proposed three-satellite regional time transfer system and enhancement for GPS covering Japan, the first demonstration satellite was launched in September 2010.[14]

In 2011 the Government of Japan has decided to accelerate the QZSS deployment in order to reach a 4-satellite constellation by the late 2010s, while aiming at a final 7-satellite constellation in the future

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French precision navigation system. Unlike other GNSS systems, it is based on static emitting stations around the world, the receivers being on satellites, in order to precisely determine their orbital position, the system may be used also for mobile receivers on land with more limited usage and coverage. Used with traditional GNSS systems, it pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system.[17]

The two current operational low Earth orbit satellite phone networks are able to track transceiver units with accuracy of a few kilometers using doppler shift calculations from the satellite, the coordinates are sent back to the transceiver unit where they can be read using AT commands or a graphical user interface.[18][19] This can also be used by the gateway to enforce restrictions on geographically bound calling plans.

Automotive navigation system
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An automotive navigation system is part of the automobile controls or a third party add-on used to find direction in an automobile. It typically uses a navigation device to get its position data which is then correlated to a position on a road. When directions are needed routing can be calculated, on the fly traffic information can be used to adjus

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Navigation with Gosmore, an open source routing software, on a personal navigation assistant with free map data from OpenStreetMap.

Satellite
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In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are called artificial satellites to distinguish them from natural satellites such as Earths Moon. In 1957 the Soviet Union launched the worlds first artificial satellite, since then, about 6,600 satellites from more than 4

Electronics
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Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements, the science of electronics is also considered to be a branch of physics and electric

Latitude
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In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earths surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles, lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the

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A graticule on the Earth as a sphere or an ellipsoid. The lines from pole to pole are lines of constant longitude, or meridians. The circles parallel to the equator are lines of constant latitude, or parallels. The graticule determines the latitude and longitude of points on the surface. In this example meridians are spaced at 6° intervals and parallels at 4° intervals.

Altitude
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Altitude or height is defined based on the context in which it is used. As a general definition, altitude is a measurement, usually in the vertical or up direction. The reference datum also often varies according to the context, although the term altitude is commonly used to mean the height above sea level of a location, in geography the term eleva

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Vertical distance comparison

Elevation
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GIS or geographic information system is a computer system that allows for visualizing, manipulating, capturing, and storage of data with associated attributes. GIS offers better understanding of patterns and relationships of the landscape at different scales, tools inside the GIS allow for manipulation of data for spatial analysis or cartography. A

Time signal
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A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks, however, busy ports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for n

Line-of-sight propagation
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Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves which travel in a direct path from the source to the receiver. Electromagnetic transmission includes light emissions traveling in a straight line, the rays or waves may be diffracted, refracted, reflected, or absorbed by atmosph

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Line of sight propagation to an antenna

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R is the radius of the Earth, h is the height of the transmitter (exaggerated), d is the line of sight distance

Radio
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude mo

United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean,

Global Positioning System
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The Global Positioning System is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. The GPS system operates independently of any telephonic or internet reception, the GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. T

Russia
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Russia, also officially the Russian Federation, is a country in Eurasia. The European western part of the country is more populated and urbanised than the eastern. Russias capital Moscow is one of the largest cities in the world, other urban centers include Saint Petersburg, Novosibirsk, Yekaterinburg, Nizhny Novgorod. Extending across the entirety

GLONASS
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GLONASS, or Global Navigation Satellite System, is a space-based satellite navigation system operating in the radionavigation-satellite service and used by the Russian Aerospace Defence Forces. It provides an alternative to GPS and is the second alternative navigational system in operation with global coverage, smartphones generally tend to use the

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President Vladimir Putin with a GLONASS car navigation device. As President, Putin paid special attention to the development of GLONASS.

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A Russian military rugged, combined GLONASS/GPS receiver

European Union
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The European Union is a political and economic union of 28 member states that are located primarily in Europe. It has an area of 4,475,757 km2, the EU has developed an internal single market through a standardised system of laws that apply in all member states. Within the Schengen Area, passport controls have been abolished, a monetary union was es

Galileo (satellite navigation)
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The €5 billion project is named after the Italian astronomer Galileo Galilei. The use of basic Galileo services will be free and open to everyone, the higher-precision capabilities will be available for paying commercial users. Galileo is intended to provide horizontal and vertical measurements within 1-metre precision. Galileo is to provide a new

China
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China, officially the Peoples Republic of China, is a unitary sovereign state in East Asia and the worlds most populous country, with a population of over 1.381 billion. The state is governed by the Communist Party of China and its capital is Beijing, the countrys major urban areas include Shanghai, Guangzhou, Beijing, Chongqing, Shenzhen, Tianjin

BeiDou Navigation Satellite System
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and

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The BeiDou system's logo

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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.

Compass navigation system
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and

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The BeiDou system's logo

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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.

India
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India, officially the Republic of India, is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and it is bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast. It shares land borders with Pakistan to the west, China, Nepal, and Bhutan to

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Writing the will and testament of the Mughal king court in Persian, 1590–1595

France
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France, officially the French Republic, is a country with territory in western Europe and several overseas regions and territories. The European, or metropolitan, area of France extends from the Mediterranean Sea to the English Channel and the North Sea, Overseas France include French Guiana on the South American continent and several island territ

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One of the Lascaux paintings: a horse – Dordogne, approximately 18,000 BC

Japan
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Japan is a sovereign island nation in Eastern Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asia Mainland and stretches from the Sea of Okhotsk in the north to the East China Sea, the kanji that make up Japans name mean sun origin. 日 can be read as ni and means sun while 本 can be read as hon, or pon, Japan is often referr

Satellite constellation
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A satellite constellation is a group of artificial satellites working in concert. Many LEO satellites are needed to maintain continuous coverage over an area and this contrasts with geostationary satellites, where a single satellite, moving at the same angular velocity as the rotation of the Earths surface, provides permanent coverage over a large

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The GPS constellation calls for 24 satellites to be distributed equally among six circular orbital planes

Medium Earth orbit
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Medium Earth orbit, sometimes called intermediate circular orbit, is the region of space around the Earth above low Earth orbit and below geostationary orbit. The most common use for satellites in this region is for navigation, communication, the most common altitude is approximately 20,200 kilometres ), which yields an orbital period of 12 hours,

Orbital inclination
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Orbital inclination measures the tilt of an objects orbit around a celestial body. It is expressed as the angle between a plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the orbit is the same as the Earths equatorial plane. The general case is that

Satellite Based Augmentation System
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There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information. A satellite-based augmentation system is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages, such systems are commonly composed of multiple g

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Service areas of satellite-based augmentation systems (SBAS).

Ground Based Augmentation System
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There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information. A satellite-based augmentation system is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages, such systems are commonly composed of multiple g

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Service areas of satellite-based augmentation systems (SBAS).

Wide Area Augmentation System
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Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area. It may be enhanced with the Local Area Augmentation System in critical areas. WAAS uses a network of ground-based reference stations, in North America and Hawaii and those satellites broad

European Geostationary Navigation Overlay Service
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The European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo satellite navigation systems by reporting on the reliability and accuracy of their positioning data, EGNOS consists of a network o

Multi-Functional Transport Satellite
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Multifunctional Transport Satellites are a series of weather and aviation control satellites. They replace the GMS-5 satellite, also known as Himawari 5 and they can provide imagery in five wavelength bands — visible and four infrared, including the water vapour channel. The visible light camera has a resolution of 1 km, the cameras have 4 km. The

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MTSAT-1 Himawari 6

Local Area Augmentation System
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The Local Area Augmentation System is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a location at the airport. This data is used to formulate a message, which is then transmitted to users via a VHF Data Link. A receiver on an air

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LAAS Architecture

StarFire (navigation system)
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StarFire is a wide-area differential GPS developed by John Deeres NavCom and precision farming groups.5 cm. StarFire is similar to the FAAs differential GPS Wide Area Augmentation System, StarFire came about after a meeting in 1994 among John Deere engineers who were attempting to chart a course for future developments. At the time, a number of com

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Two Navcom SF-2040G Receivers

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Survey crew using the pole-mounted Navcom SF-2040G receiver

GPS-aided geo-augmented navigation
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The GPS Aided GEO Augmented Navigation is an implementation of a regional satellite-based augmentation system by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals and it will be able to help pilots to navigate in the Indian airspace by an accuracy of 3 m. This will be helpful for landing

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Organisations

Beidou navigation system
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and

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The BeiDou system's logo

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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.

Indian Regional Navigation Satellite System
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The Indian government approved the project in May 2006. The constellation of seven NAVIC satellites is already in orbit and the system is expected to be operational from September 2016, NAVIC will provide two levels of service, the standard positioning service will be open for civilian use, and a restricted service for authorized users. As part of

QZSS
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The first satellite Michibiki was launched on 11 September 2010. Full operational status was expected by 2013, in March 2013, Japans Cabinet Office announced the expansion of the Quasi-Zenith Satellite System from three satellites to four. The $526 million contract with Mitsubishi Electric for the construction of three satellites is slated for laun

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Quasi-Zenith satellite orbit

Differential GPS
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DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the GPS satellite systems and the known fixed positions. These stations broadcast the difference between the measured satellite pseudoranges and actual pseudoranges, and receiver stations may correct their pseudoranges by the

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Transportable DGPS reference station Baseline HD by CLAAS for use in satellite-assisted steering systems in modern agriculture

Real Time Kinematic
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Real Time Kinematic satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems such as GPS, GLONASS, Galileo, and BeiDou. With reference to GPS in particular, the system is referred to as Carrier-Phase Enhancement. It has applications in land survey, hydrographic survey, and i

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North SmaRTK GNSS RTK Receiver being used to survey the forest population in Switzerland.

Radio navigation
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Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth. Like radiolocation, it is a type of radiodetermination and these systems used some form of directional radio antenna to determine the location of a broadcast station on the ground. Conventional navigation techniques are use

Decca Navigator System
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The Decca Navigator System was a hyperbolic radio navigation system which allowed ships and aircraft to determine their position by receiving radio signals from fixed navigational beacons. The system used phase comparison of low frequencies from 70 to 129 kHz, as opposed to pulse timing systems like Gee and this made it much easier to implement the

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The display head, or "decometer bowl", of a Decca Navigator Mk 12 (ca. 1962). Not shown is the much larger receiver unit.

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An ap Decca receiver Mk II from the 1980s which could be purchased instead of leased. It could store 25 waypoints.

LORAN

GEE
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Gee, sometimes written GEE, was a radio navigation system used by the Royal Air Force during World War II. It measured the time delay between two signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up to about 350 miles. It was the first hyperbolic system to be used operationally. For large, fixed targets, like th

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GEE airborne equipment, with the R1355 receiver on the left and the Indicator Unit Type 62A on the right. The 'scope shows a simulated display, including the "ghost" A1 signal.

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GEE control bays

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GEE transmitter

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Low-level photo of a light mobile Gee station operating in a field near Roermond, Holland. These forward stations provided Gee coverage deeper into Germany, as well as strong signals for aircraft returning to bases in western Europe.

Omega Navigation System
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OMEGA was the first truly global-range radio navigation system, operated by the United States in cooperation with six partner nations. It became operational around 1971 and was shut down in 1997 in favour of the Global Positioning Satellite system, taking a fix in any navigation system requires the determination of two measurements. Typically these

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The Communications Control Link building of the Naval Radio Station at Haiku, part of the Kaneohe Omega Transmitter, 1987

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based on NASA Worldwind-globe [1] - location of Omega-transmitter A in Norway (distances)

Longwave
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In radio, longwave, also written as long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an one, dating from the early 20th century, when the radio spectrum was considered to consist of long, medium. Most modern radio systems and devices use wavelengths which would

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The tuning dial on a 1940s radio, showing longwave wavelengths between 800 and 2000 metres, corresponding to frequencies between 375 and 150 kHz

Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or rad

Fix (position)
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In position fixing navigation, a position fix or simply a fix is a position derived from measuring external reference points. A visual fix can be made by using any sighting device with a bearing indicator, two or more objects of known position are sighted, and the bearings recorded. Bearing lines are plotted on a chart through the locations of the

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Visual fix by three bearings plotted on a nautical chart

Transit (satellite)
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The Transit system, also known as NAVSAT or NNSS, was the first satellite navigation system to be used operationally. The system was used by the U. S. Transit provided continuous navigation satellite service from 1964, initially for Polaris submarines and they were able to determine Sputniks orbit by analyzing the Doppler shift of its radio signals

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Operational Transit satellite

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Transit 2A with GRAB 1 atop during launch preparations

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Transit-1-Satellite Prototype

Doppler effect
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The Doppler effect is the change in frequency or wavelength of a wave for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, a common example of Doppler shift is the change of pitch heard when a vehicle sounding a siren or horn approaches, passes, and recedes fro

US Naval Observatory
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The USNO operates the Master Clock, which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, aside from its scientific mission, a house located within the Naval Observatory complex serves as the official residence of

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Aerial view of the U.S. Naval Observatory

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The Seal of the USNO with a quote from the Astronomicon, Adde gubernandi studium: Pervenit in astra, et pontum caelo conjunxit, "Increase the study of navigation: it arrives in the stars, and marries the sea with heaven"

Ephemeris
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In astronomy and celestial navigation, an ephemeris gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times. Historically, positions were given as printed tables of values, given at intervals of date. Modern ephemerides are often computed electronically from mathematical m

Atomic clock
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The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics, it uses the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature, currently, the most accurate atomic clocks first cool the atoms to near absolute zero tem

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FOCS 1, a continuous cold caesium fountain atomic clock in Switzerland, started operating in 2004 at an uncertainty of one second in 30 million years.

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The master atomic clock ensemble at the U.S. Naval Observatory in Washington, D.C., which provides the time standard for the U.S. Department of Defense. The rack mounted units in the background are Symmetricom (formerly HP) 5071A caesium beam clocks. The black units in the foreground are Symmetricom (formerly Sigma-Tau) MHM-2010 hydrogen maser standards.

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Chip-scale atomic clocks, such as this one unveiled in 2004, are expected to greatly improve GPS location.

Trilateration

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Figure 1. The plane z = 0, showing the three sphere centers, P 1, P 2, and P 3; their x, y -coordinates; and the three sphere radii, r 1, r 2, and r 3. The two intersections of the three sphere surfaces are directly in front and directly behind the point designated intersections in the z = 0 plane.

2.
The Kalman filter keeps track of the estimated state of the system and the variance or uncertainty of the estimate. The estimate is updated using a state transition model and measurements. denotes the estimate of the system's state at time step k before the k -th measurement y k has been taken into account; is the corresponding uncertainty.

GNSS applications

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A GPS receiver in civilian automobile use.

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A GPS unit showing basic way point and tracking information which is typically required for outdoor sport and recreational use

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In the computer game Freeciv, completely unexplored areas are fully black, while currently unobserved areas are covered in a grey shroud.

Geostationary Earth Orbit

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A 5 × 6 degree view of a part of the geostationary belt, showing several geostationary satellites. Those with inclination 0 degrees form a diagonal belt across the image; a few objects with small inclinations to the Equator are visible above this line. The satellites are pinpoint, while stars have created small trails due to the Earth's rotation.

2.
To an observer on the rotating Earth, both satellites appear stationary in the sky at their respective locations.

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The Hubble Space Telescope as seen from the departing Space ShuttleAtlantis, flying Servicing Mission 4 (STS-125), the fifth and final human spaceflight to it.

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Grinding of Hubble's primary mirror at Perkin-Elmer, March 1979

3.
The backup mirror, by Kodak; its inner support structure can be seen because it is not coated with a reflective surface.

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The OTA, metering truss, and secondary baffle are visible in this image of Hubble during early construction.

Iridium constellation

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Replica of an Iridium satellite

Van Allen radiation belt

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Jupiter's variable radiation belts

3.
Laboratory simulation of the Van Allen belt's influence on the Solar Wind; these aurora-like Birkeland currents were created by the scientist Kristian Birkeland in his terrella, a magnetized anode globe in an evacuated chamber

4.
Cutaway drawing of two radiation belts around Earth: the inner belt (red) dominated by protons and the outer one (blue) by electrons. Image Credit: NASA

Beidou Navigation Satellite System
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and

1.
The BeiDou system's logo

2.
Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.

1.
A 5 × 6 degree view of a part of the geostationary belt, showing several geostationary satellites. Those with inclination 0 degrees form a diagonal belt across the image; a few objects with small inclinations to the Equator are visible above this line. The satellites are pinpoint, while stars have created small trails due to the Earth's rotation.

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To an observer on the rotating Earth, both satellites appear stationary in the sky at their respective locations.

Geosynchronous orbit

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Syncom 2

2.
A geostationary satellite above a marked spot on the Equator. An observer on the marked spot will see the satellite remain directly overhead unlike other celestial objects which sweep across the sky.

2.
Sidereal time vs solar time. Above left: a distant star (the small red circle) and the Sun are at culmination, on the local meridian. Centre: only the distant star is at culmination (a mean sidereal day). Right: a few minutes later the Sun is on the local meridian again. A solar day is complete.

1.
Automotive navigation system
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An automotive navigation system is part of the automobile controls or a third party add-on used to find direction in an automobile. It typically uses a navigation device to get its position data which is then correlated to a position on a road. When directions are needed routing can be calculated, on the fly traffic information can be used to adjust the route. Automotive navigation systems represent a convergence of a number of diverse technologies many of which have available for many years. Limitations such as batteries, display, and processing power had to be overcome before the product became commercially viable, etak made an early system that used map-matching to improve on dead reckoning instrumentation. Digital map information was stored on cassette tapes. 1966, General Motors Research was working on a non-satellite-based navigation, after initial tests GM found that it was not a scalable or practical way to provide navigation assistance. Decades later, however, the concept would be reborn as OnStar,1980, Electronic Auto Compass with new mechanism on the Toyota Crown. 1981, navigation computer on the Toyota Celica,1987, Toyota introduced the Worlds first CD-ROM-based navigation system on the Toyota Crown. 1990, Mazda Eunos Cosmo became the first car with built-in GPS-navigation system 1991,1991, Mitsubishi introduced GPS car navigation on the Mitsubishi Debonair. 1992, Voice assisted GPS navigation system on the Toyota Celsior, bitMAP attends Comdex in Las Vegas the same year, but doesnt manage to market itself properly. 1994, BMW7 series E38 first European model featuring GPS sat nav, the navigation system was developed in cooperation with Philips. 1995, Oldsmobile introduced the first GPS navigation system available in a United States production car,1995, Device called Mobile Assistant or short, MASS, produced by Munich-based company ComRoad AG, won the title Best Product in Mobile Computing on CeBit by magazine Byte. It offered turn-by-turn navigation via wireless connection, with both GPS and speed sensor in the car. Street names or numbers and house numbers are encoded as geographic coordinates so that the user can find some desired destination by street address, points of interest are stored with their geographic coordinates. Formats are almost uniformly proprietary, there is no standard for satellite navigation maps, although some companies are trying to address this with SDAL. Map data vendors such as Tele Atlas and Navteq create the map in a Geographic Data Files format. GDF is not a CD standard for car navigation systems, GDF is used and converted onto the CD-ROM in the internal format of the navigation system

Automotive navigation system
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Navigation with Gosmore, an open source routing software, on a personal navigation assistant with free map data from OpenStreetMap.

2.
Satellite
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In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are called artificial satellites to distinguish them from natural satellites such as Earths Moon. In 1957 the Soviet Union launched the worlds first artificial satellite, since then, about 6,600 satellites from more than 40 countries have been launched. According to a 2013 estimate,3,600 remained in orbit, of those, about 1,000 were operational, the rest have lived out their useful lives and become space debris. Approximately 500 operational satellites are in orbit,50 are in medium-Earth orbit. A few large satellites have been launched in parts and assembled in orbit. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, Satellites are used for many purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, well-known classes include low Earth orbit, polar orbit, and geostationary orbit. A launch vehicle is a rocket that throws a satellite into orbit, usually it lifts off from a launch pad on land. Some are launched at sea from a submarine or a mobile maritime platform, Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control, the first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale, The Brick Moon. The idea surfaced again in Jules Vernes The Begums Fortune, in 1903, Konstantin Tsiolkovsky published Exploring Space Using Jet Propulsion Devices, which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the speed required for a minimal orbit. In 1928, Herman Potočnik published his book, The Problem of Space Travel — The Rocket Motor. He described the use of orbiting spacecraft for observation of the ground, in a 1945 Wireless World article, the English science fiction writer Arthur C. Clarke described in detail the possible use of communications satellites for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet, the first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4,1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer. This in turn triggered the Space Race between the Soviet Union and the United States, Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere

3.
Electronics
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Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements, the science of electronics is also considered to be a branch of physics and electrical engineering. The ability of electronic devices to act as switches makes digital information processing possible, until 1950 this field was called radio technology because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes. Today, most electronic devices use semiconductor components to perform electron control and this article focuses on engineering aspects of electronics. Components are generally intended to be connected together, usually by being soldered to a circuit board. Components may be packaged singly, or in more complex groups as integrated circuits, some common electronic components are capacitors, inductors, resistors, diodes, transistors, etc. Components are often categorized as active or passive, vacuum tubes were among the earliest electronic components. They were almost solely responsible for the revolution of the first half of the Twentieth Century. They took electronics from parlor tricks and gave us radio, television, phonographs, radar, long distance telephony and they played a leading role in the field of microwave and high power transmission as well as television receivers until the middle of the 1980s. Since that time, solid state devices have all but completely taken over, vacuum tubes are still used in some specialist applications such as high power RF amplifiers, cathode ray tubes, specialist audio equipment, guitar amplifiers and some microwave devices. The 608 contained more than 3,000 germanium transistors, thomas J. Watson Jr. ordered all future IBM products to use transistors in their design. From that time on transistors were almost exclusively used for computer logic, circuits and components can be divided into two groups, analog and digital. A particular device may consist of circuitry that has one or the other or a mix of the two types, most analog electronic appliances, such as radio receivers, are constructed from combinations of a few types of basic circuits. Analog circuits use a range of voltage or current as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a circuit can be defined as anything from a single component, analog circuits are sometimes called linear circuits although many non-linear effects are used in analog circuits such as mixers, modulators, etc. Good examples of analog circuits include vacuum tube and transistor amplifiers, one rarely finds modern circuits that are entirely analog. These days analog circuitry may use digital or even microprocessor techniques to improve performance and this type of circuit is usually called mixed signal rather than analog or digital. Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation, an example is the comparator which takes in a continuous range of voltage but only outputs one of two levels as in a digital circuit

4.
Latitude
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In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earths surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles, lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the location of features on the surface of the Earth. Without qualification the term latitude should be taken to be the latitude as defined in the following sections. Also defined are six auxiliary latitudes which are used in special applications, there is a separate article on the History of latitude measurements. Two levels of abstraction are employed in the definition of latitude and longitude, in the first step the physical surface is modelled by the geoid, a surface which approximates the mean sea level over the oceans and its continuation under the land masses. The second step is to approximate the geoid by a mathematically simpler reference surface, the simplest choice for the reference surface is a sphere, but the geoid is more accurately modelled by an ellipsoid. The definitions of latitude and longitude on such surfaces are detailed in the following sections. Lines of constant latitude and longitude together constitute a graticule on the reference surface, latitude and longitude together with some specification of height constitute a geographic coordinate system as defined in the specification of the ISO19111 standard. This is of importance in accurate applications, such as a Global Positioning System, but in common usage, where high accuracy is not required. In English texts the latitude angle, defined below, is denoted by the Greek lower-case letter phi. It is measured in degrees, minutes and seconds or decimal degrees, the precise measurement of latitude requires an understanding of the gravitational field of the Earth, either to set up theodolites or to determine GPS satellite orbits. The study of the figure of the Earth together with its field is the science of geodesy. These topics are not discussed in this article and this article relates to coordinate systems for the Earth, it may be extended to cover the Moon, planets and other celestial objects by a simple change of nomenclature. The primary reference points are the poles where the axis of rotation of the Earth intersects the reference surface, the plane through the centre of the Earth and perpendicular to the rotation axis intersects the surface at a great circle called the Equator. Planes parallel to the plane intersect the surface in circles of constant latitude. The Equator has a latitude of 0°, the North Pole has a latitude of 90° North, the latitude of an arbitrary point is the angle between the equatorial plane and the radius to that point. The latitude, as defined in this way for the sphere, is termed the spherical latitude

Latitude
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A graticule on the Earth as a sphere or an ellipsoid. The lines from pole to pole are lines of constant longitude, or meridians. The circles parallel to the equator are lines of constant latitude, or parallels. The graticule determines the latitude and longitude of points on the surface. In this example meridians are spaced at 6° intervals and parallels at 4° intervals.

5.
Altitude
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Altitude or height is defined based on the context in which it is used. As a general definition, altitude is a measurement, usually in the vertical or up direction. The reference datum also often varies according to the context, although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage. Vertical distance measurements in the direction are commonly referred to as depth. In aviation, the altitude can have several meanings, and is always qualified by explicitly adding a modifier. Parties exchanging altitude information must be clear which definition is being used, aviation altitude is measured using either mean sea level or local ground level as the reference datum. When flying at a level, the altimeter is always set to standard pressure. On the flight deck, the instrument for measuring altitude is the pressure altimeter. There are several types of altitude, Indicated altitude is the reading on the altimeter when it is set to the local barometric pressure at mean sea level. In UK aviation radiotelephony usage, the distance of a level, a point or an object considered as a point, measured from mean sea level. Absolute altitude is the height of the aircraft above the terrain over which it is flying and it can be measured using a radar altimeter. Also referred to as radar height or feet/metres above ground level, true altitude is the actual elevation above mean sea level. It is indicated altitude corrected for temperature and pressure. Height is the elevation above a reference point, commonly the terrain elevation. Pressure altitude is used to indicate flight level which is the standard for reporting in the U. S. in Class A airspace. Pressure altitude and indicated altitude are the same when the setting is 29.92 Hg or 1013.25 millibars. Density altitude is the altitude corrected for non-ISA International Standard Atmosphere atmospheric conditions, aircraft performance depends on density altitude, which is affected by barometric pressure, humidity and temperature. On a very hot day, density altitude at an airport may be so high as to preclude takeoff and these types of altitude can be explained more simply as various ways of measuring the altitude, Indicated altitude – the altitude shown on the altimeter

Altitude
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Vertical distance comparison

6.
Elevation
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GIS or geographic information system is a computer system that allows for visualizing, manipulating, capturing, and storage of data with associated attributes. GIS offers better understanding of patterns and relationships of the landscape at different scales, tools inside the GIS allow for manipulation of data for spatial analysis or cartography. A topographical map is the type of map used to depict elevation. In a Geographic Information System, digital models are commonly used to represent the surface of a place. Digital terrain models are another way to represent terrain in GIS, USGS is developing a 3D Elevation Program to keep up with growing needs for high quality topographic data. 3DEP is a collection of enhanced elevation data in the form of high quality LiDAR data over the conterminous United States, Hawaii, there are three bare earth DEM layers in 3DEP which are nationally seamless at the resolution of 1/3,1, and 2 arcseconds. This map is derived from GTOPO30 data that describes the elevation of Earths terrain at intervals of 30 arcseconds and it uses color and shading instead of contour lines to indicate elevation. Hypsography is the study of the distribution of elevations on the surface of the Earth, the term originates from the Greek word ὕψος hypsos meaning height. Most often it is used only in reference to elevation of land, related to the term hypsometry, the measurement of these elevations of a planets solid surface are taken relative to mean datum, except for Earth which is taken relative to the sea level. In the troposphere, temperatures decrease with altitude and this lapse rate is approximately 6.5 °C/km. S

7.
Time signal
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A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks, however, busy ports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical telegraphs allowed widespread and precise distribution of time signals from central observatories, Railways were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Special purpose radio time signal stations transmit a signal that allows automatic synchronization of clocks, today, GPS navigation radio signals are used to precisely distribute time signals over much of the world. There are many commercially available radio controlled clocks available to indicate the local time. Computers often set their time from an atomic clock source. Where this is not available, a locally connected GPS receiver can set the time using a software application. There are several such applications available to download from the internet, One sort of public time signal is a striking clock. These clocks are only as good as the clockwork that activates them, until modern times, a public clock such as Big Ben was the only time standard the general public needed. When more accurate time signals were required in navigation, a number of traditional audible or visible time signals were established so navigators could check their marine chronometers and these public time signals were formerly established in many seaport cities. In Vancouver, British Columbia, a 9 OClock Gun is still shot every night at 9 pm, the 9,00 pm firing was later established as a time signal for the general population. Until a time gun was installed, the nearby Brockton Point lighthouse keeper detonated a stick of dynamite, elsewhere in Canada, a Noon Gun is fired daily from the citadels in Halifax and Quebec City. In the same manner, a gun has been fired in Cape Town, South Africa. The gun is fired daily from the Lion Battery at Signal Hill, a cannon was fired at one oclock every weekday at Liverpool, England, at the Castle in Edinburgh, Scotland, and also at Perth in Australia to establish the time. The Edinburgh One OClock Gun is still in operation, a cannon located at the top of Santa Lucia Hill, in Santiago, Chile, is shot every noon. In Rome, on the Janiculum, a hill west of the Tiber since 1904 a cannon is fired daily at noon towards the river as a time signal and this was introduced in 1847 by Pope Pius IX to synchronise all the church bells of Rome. It was situated in Castel SantAngelo until 1903 when it was moved to Monte Mario for a few months until it was placed in its current position. The cannon was silenced from the start of WWII for about twenty years until 21 April 1959, the 2712th anniversary of Romes founding, and has been in use since then

8.
Line-of-sight propagation
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Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves which travel in a direct path from the source to the receiver. Electromagnetic transmission includes light emissions traveling in a straight line, the rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles. In contrast to line-of-sight propagation, at low frequency due to radio waves can travel as ground waves. This enables AM broadcast radio stations to transmit beyond the horizon, however, at frequencies above 30 MHz and in lower levels of the atmosphere, neither of these effects are significant. Thus, any obstruction between the antenna and the receiving antenna will block the signal, just like the light that the eye may sense. The farthest possible point of propagation is referred to as the radio horizon, in practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal. Broadcast FM radio, at low frequencies of around 100 MHz, are less affected by the presence of buildings. Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow, if a direct visual fix cannot be taken, it is important to take into account the curvature of the Earth when calculating line-of-sight from maps. Designs for microwave used to use 4/3 earth radius to compute clearances along the path, the presence of objects not in the direct visual line of sight can interfere with radio transmission. This is caused by diffraction effects, for the best propagation, reflected radiation from the ground plane also acts to cancel out the direct signal. This effect, combined with the free-space r−2 propagation loss to a r−4 propagation loss and this effect can be reduced by raising either or both antennas further from the ground, the reduction in loss achieved is known as height gain. Although the frequencies used by mobile phones are in the line-of-sight range, for mobile phone services, these problems are tackled using, rooftop or hilltop positioning of base stations many base stations. A phone can typically see at least three, and usually as many as six at any given time, sectorized antennas at the base stations. Instead of one antenna with omnidirectional coverage, the station may use as few as 3 or as many as 32 separate antennas and this allows the base station to use a directional antenna that is pointing at the user, which improves the signal to noise ratio. If the user moves from one sector to another, the base station automatically selects the proper antenna. Electromagnetic radiation is blocked where the wavelength is longer than any gaps and this means that windowless metal enclosures will completely block cell signs, such as elevator cabins, and parts of trains, cars, and ships. The same problem can affect signals in buildings with steel reinforcement. The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth, if the Earth was a perfect sphere and there was no atmosphere, the radio horizon would be a circle

Line-of-sight propagation
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Line of sight propagation to an antenna
Line-of-sight propagation
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R is the radius of the Earth, h is the height of the transmitter (exaggerated), d is the line of sight distance

9.
Radio
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal

10.
United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci

11.
Global Positioning System
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The Global Positioning System is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. The GPS system operates independently of any telephonic or internet reception, the GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, however, the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War. The U. S. Department of Defense developed the system and it became fully operational in 1995. Roger L. Easton of the Naval Research Laboratory, Ivan A, getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes, in 2000, the U. S. Congress authorized the modernization effort, GPS III. In addition to GPS, other systems are in use or under development, mainly because of a denial of access. The Russian Global Navigation Satellite System was developed contemporaneously with GPS, GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within two meters. There are also the European Union Galileo positioning system and Chinas BeiDou Navigation Satellite System, special and general relativity predict that the clocks on the GPS satellites would be seen by the Earths observers to run 38 microseconds faster per day than the clocks on the Earth. The GPS calculated positions would quickly drift into error, accumulating to 10 kilometers per day, the relativistic time effect of the GPS clocks running faster than the clocks on earth was corrected for in the design of GPS. The Soviet Union launched the first man-made satellite, Sputnik 1, two American physicists, William Guier and George Weiffenbach, at Johns Hopkinss Applied Physics Laboratory, decided to monitor Sputniks radio transmissions. Within hours they realized that, because of the Doppler effect, the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the users location and this led them and APL to develop the TRANSIT system. In 1959, ARPA also played a role in TRANSIT, the first satellite navigation system, TRANSIT, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour, in 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based OMEGA navigation system, based on comparison of signal transmission from pairs of stations. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy, during the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded and it is also the reason for the ultra secrecy at that time

12.
Russia
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Russia, also officially the Russian Federation, is a country in Eurasia. The European western part of the country is more populated and urbanised than the eastern. Russias capital Moscow is one of the largest cities in the world, other urban centers include Saint Petersburg, Novosibirsk, Yekaterinburg, Nizhny Novgorod. Extending across the entirety of Northern Asia and much of Eastern Europe, Russia spans eleven time zones and incorporates a range of environments. It shares maritime borders with Japan by the Sea of Okhotsk, the East Slavs emerged as a recognizable group in Europe between the 3rd and 8th centuries AD. Founded and ruled by a Varangian warrior elite and their descendants, in 988 it adopted Orthodox Christianity from the Byzantine Empire, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Rus ultimately disintegrated into a number of states, most of the Rus lands were overrun by the Mongol invasion. The Soviet Union played a role in the Allied victory in World War II. The Soviet era saw some of the most significant technological achievements of the 20th century, including the worlds first human-made satellite and the launching of the first humans in space. By the end of 1990, the Soviet Union had the second largest economy, largest standing military in the world. It is governed as a federal semi-presidential republic, the Russian economy ranks as the twelfth largest by nominal GDP and sixth largest by purchasing power parity in 2015. Russias extensive mineral and energy resources are the largest such reserves in the world, making it one of the producers of oil. The country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction, Russia is a great power as well as a regional power and has been characterised as a potential superpower. The name Russia is derived from Rus, a state populated mostly by the East Slavs. However, this name became more prominent in the later history, and the country typically was called by its inhabitants Русская Земля. In order to distinguish this state from other states derived from it, it is denoted as Kievan Rus by modern historiography, an old Latin version of the name Rus was Ruthenia, mostly applied to the western and southern regions of Rus that were adjacent to Catholic Europe. The current name of the country, Россия, comes from the Byzantine Greek designation of the Kievan Rus, the standard way to refer to citizens of Russia is Russians in English and rossiyane in Russian. There are two Russian words which are translated into English as Russians

13.
GLONASS
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GLONASS, or Global Navigation Satellite System, is a space-based satellite navigation system operating in the radionavigation-satellite service and used by the Russian Aerospace Defence Forces. It provides an alternative to GPS and is the second alternative navigational system in operation with global coverage, smartphones generally tend to use the same chipsets and the versions used since 2015 receive GLONASS signals and positioning information along with GPS. Since 2012, GLONASS was the second most used positioning system in mobile phones after GPS, the system has the advantage that smartphone users receive a more accurate reception identifying location to within 2 meters. Development of GLONASS began in the Soviet Union in 1976, beginning on 12 October 1982, numerous rocket launches added satellites to the system until the constellation was completed in 1995. After a decline in capacity during the late 1990s, in 2001, under Vladimir Putins presidency, GLONASS is the most expensive program of the Russian Federal Space Agency, consuming a third of its budget in 2010. By 2010, GLONASS had achieved 100% coverage of Russias territory and in October 2011, the GLONASS satellites designs have undergone several upgrades, with the latest version being GLONASS-K. GLONASS is a satellite navigation system, providing real time position and velocity determination for military. The satellites are located in middle circular orbit at 19,100 kilometres altitude with a 64.8 degree inclination, GLONASS orbit makes it especially suited for usage in high latitudes, where getting a GPS signal can be problematic. The constellation operates in three planes, with eight evenly spaced satellites on each. A fully operational constellation with global coverage consists of 24 satellites, to get a position fix the receiver must be in the range of at least four satellites. GLONASS satellites transmit two types of signal, open standard-precision signal L1OF/L2OF, and obfuscated high-precision signal L1SF/L2SF, the signals use similar DSSS encoding and binary phase-shift keying modulation as in GPS signals.0 MHz, known as the L1 band. The center frequency is 1602 MHz + n ×0.5625 MHz, signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 and 27 dBW. The L2 band signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency 1246 MHz + n×0.4375 MHz, the pseudo-random code is generated with a 9-stage shift register operating with a period of 1 ms. The navigational message is modulated at 50 bits per second, the superframe of the open signal is 7500 bits long and consists of 5 frames of 30 seconds, taking 150 seconds to transmit the continuous message. Each frame is 1500 bits long and consists of 15 strings of 100 bits, with 85 bits for data and check-sum bits, and 15 bits for time mark. Strings 1-4 provide immediate data for the satellite, and are repeated every frame, the data include ephemeris, clock and frequency offsets. Strings 5-15 provide non-immediate data for each satellite in the constellation, with frames I-IV each describing five satellites, the almanac uses modified Keplerian parameters and is updated daily. The details of the signal have not been disclosed

GLONASS
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GLONASS logo
GLONASS
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A model of a GLONASS-K satellite displayed at CeBit 2011
GLONASS
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President Vladimir Putin with a GLONASS car navigation device. As President, Putin paid special attention to the development of GLONASS.
GLONASS
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A Russian military rugged, combined GLONASS/GPS receiver

14.
European Union
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The European Union is a political and economic union of 28 member states that are located primarily in Europe. It has an area of 4,475,757 km2, the EU has developed an internal single market through a standardised system of laws that apply in all member states. Within the Schengen Area, passport controls have been abolished, a monetary union was established in 1999 and came into full force in 2002, and is composed of 19 EU member states which use the euro currency. The EU operates through a system of supranational and intergovernmental decision-making. The EU traces its origins from the European Coal and Steel Community, the community and its successors have grown in size by the accession of new member states and in power by the addition of policy areas to its remit. While no member state has left the EU or its antecedent organisations, the Maastricht Treaty established the European Union in 1993 and introduced European citizenship. The latest major amendment to the basis of the EU. The EU as a whole is the largest economy in the world, additionally,27 out of 28 EU countries have a very high Human Development Index, according to the United Nations Development Programme. In 2012, the EU was awarded the Nobel Peace Prize, through the Common Foreign and Security Policy, the EU has developed a role in external relations and defence. The union maintains permanent diplomatic missions throughout the world and represents itself at the United Nations, the World Trade Organization, the G7, because of its global influence, the European Union has been described as an emerging superpower. After World War II, European integration was seen as an antidote to the nationalism which had devastated the continent. 1952 saw the creation of the European Coal and Steel Community, the supporters of the Community included Alcide De Gasperi, Jean Monnet, Robert Schuman, and Paul-Henri Spaak. These men and others are credited as the Founding fathers of the European Union. In 1957, Belgium, France, Italy, Luxembourg, the Netherlands and West Germany signed the Treaty of Rome and they also signed another pact creating the European Atomic Energy Community for co-operation in developing nuclear energy. Both treaties came into force in 1958, the EEC and Euratom were created separately from the ECSC, although they shared the same courts and the Common Assembly. The EEC was headed by Walter Hallstein and Euratom was headed by Louis Armand, Euratom was to integrate sectors in nuclear energy while the EEC would develop a customs union among members. During the 1960s, tensions began to show, with France seeking to limit supranational power, Jean Rey presided over the first merged Commission. In 1973, the Communities enlarged to include Denmark, Ireland, Norway had negotiated to join at the same time, but Norwegian voters rejected membership in a referendum

European Union
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In 1989, the Iron Curtain fell, enabling the union to expand further (Berlin Wall pictured).
European Union
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Flag
European Union
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2009, the Lisbon Treaty entered into force.
European Union
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The 65,993 km (41,006 mi) coastline dominates the European climate (Cyprus).

15.
Galileo (satellite navigation)
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The €5 billion project is named after the Italian astronomer Galileo Galilei. The use of basic Galileo services will be free and open to everyone, the higher-precision capabilities will be available for paying commercial users. Galileo is intended to provide horizontal and vertical measurements within 1-metre precision. Galileo is to provide a new search and rescue function as part of the MEOSAR system. Satellites will be equipped with a transponder which will relay distress signals from emergency beacons to the Rescue coordination centre, which will then initiate a rescue operation. At the same time, the system is projected to provide a signal and this latter feature is new and is considered a major upgrade compared to the existing Cospas-Sarsat system, which does not provide feedback to the user. The first Galileo test satellite, the GIOVE-A, was launched 28 December 2005, as of December 2016 the system has 18 of 30 satellites in orbit. Galileo started offering Early Operational Capability on 15 December 2016 and is expected to reach Full Operational Capability in 2019, the complete 30-satellite Galileo system is expected by 2020. In 1999, the different concepts of the three main contributors of ESA for Galileo were compared and reduced to one by a joint team of engineers from all three countries. The first stage of the Galileo programme was agreed upon officially on 26 May 2003 by the European Union, the system is intended primarily for civilian use, unlike the more military-orientated systems of the United States, Russia, and China. The European system will only be subject to shutdown for military purposes in extreme circumstances and it will be available at its full precision to both civil and military users. On 17 January 2002, a spokesman for the stated that, as a result of US pressure and economic difficulties. A few months later, however, the situation changed dramatically, European Union member states decided it was important to have a satellite-based positioning and timing infrastructure that the US could not easily turn off in times of political conflict. The European Union and the European Space Agency agreed in March 2002 to fund the project, the starting cost for the period ending in 2005 is estimated at €1.1 billion. The required satellites were to be launched between 2011 and 2014, with the system up and running and under control from 2019. The final cost is estimated at €3 billion, including the infrastructure on Earth, the plan was for private companies and investors to invest at least two-thirds of the cost of implementation, with the EU and ESA dividing the remaining cost. The base Open Service is to be available without charge to anyone with a Galileo-compatible receiver, by early 2011 costs for the project had run 50% over initial estimates. Galileo is intended to be an EU civilian GNSS that allows all users access to it, initially GPS reserved the highest quality signal for military use, and the signal available for civilian use was intentionally degraded

Galileo (satellite navigation)
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Headquarters of the Galileo system in Prague
Galileo (satellite navigation)
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Galileo
Galileo (satellite navigation)
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A December 2001 letter from U.S. Deputy Secretary of DefensePaul Wolfowitz to the Ministers of the EU states as part of the US- lobbying campaign against Galileo
Galileo (satellite navigation)
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Galileo launch on a Soyuz rocket, 21 October 2011

16.
China
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China, officially the Peoples Republic of China, is a unitary sovereign state in East Asia and the worlds most populous country, with a population of over 1.381 billion. The state is governed by the Communist Party of China and its capital is Beijing, the countrys major urban areas include Shanghai, Guangzhou, Beijing, Chongqing, Shenzhen, Tianjin and Hong Kong. China is a power and a major regional power within Asia. Chinas landscape is vast and diverse, ranging from forest steppes, the Himalaya, Karakoram, Pamir and Tian Shan mountain ranges separate China from much of South and Central Asia. The Yangtze and Yellow Rivers, the third and sixth longest in the world, respectively, Chinas coastline along the Pacific Ocean is 14,500 kilometers long and is bounded by the Bohai, Yellow, East China and South China seas. China emerged as one of the worlds earliest civilizations in the basin of the Yellow River in the North China Plain. For millennia, Chinas political system was based on hereditary monarchies known as dynasties, in 1912, the Republic of China replaced the last dynasty and ruled the Chinese mainland until 1949, when it was defeated by the communist Peoples Liberation Army in the Chinese Civil War. The Communist Party established the Peoples Republic of China in Beijing on 1 October 1949, both the ROC and PRC continue to claim to be the legitimate government of all China, though the latter has more recognition in the world and controls more territory. China had the largest economy in the world for much of the last two years, during which it has seen cycles of prosperity and decline. Since the introduction of reforms in 1978, China has become one of the worlds fastest-growing major economies. As of 2016, it is the worlds second-largest economy by nominal GDP, China is also the worlds largest exporter and second-largest importer of goods. China is a nuclear weapons state and has the worlds largest standing army. The PRC is a member of the United Nations, as it replaced the ROC as a permanent member of the U. N. Security Council in 1971. China is also a member of numerous formal and informal multilateral organizations, including the WTO, APEC, BRICS, the Shanghai Cooperation Organization, the BCIM, the English name China is first attested in Richard Edens 1555 translation of the 1516 journal of the Portuguese explorer Duarte Barbosa. The demonym, that is, the name for the people, Portuguese China is thought to derive from Persian Chīn, and perhaps ultimately from Sanskrit Cīna. Cīna was first used in early Hindu scripture, including the Mahābhārata, there are, however, other suggestions for the derivation of China. The official name of the state is the Peoples Republic of China. The shorter form is China Zhōngguó, from zhōng and guó and it was then applied to the area around Luoyi during the Eastern Zhou and then to Chinas Central Plain before being used as an occasional synonym for the state under the Qing

17.
BeiDou Navigation Satellite System
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering services, mainly for customers in China and neighboring regions. It became operational in China in December 2011, with 10 satellites in use and it is planned to begin serving global customers upon its completion in 2020. In-mid 2015, China started the build-up of the third generation BeiDou system in the global coverage constellation, the first BDS-3 satellite was launched 30 September 2015. As of March 2016,4 BDS-3 in-orbit validation satellites have been launched, the official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Běidǒu, the name literally means Northern Dipper, the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris, as such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun, the third satellite, BeiDou-1C, was put into orbit on 25 May 2003. The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system. On 2 November 2006, China announced that from 2008 BeiDou would offer a service with an accuracy of 10 meters, timing of 0.2 microseconds. In February 2007, the fourth and last satellite of the BeiDou-1 system and it was reported that the satellite had suffered from a control system malfunction but was then fully restored. In April 2007, the first satellite of BeiDou-2, namely Compass-M1 was successfully put into its working orbit, the second BeiDou-2 constellation satellite Compass-G2 was launched on 15 April 2009. On 2 June 2010, the satellite was launched successfully into orbit. The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010, three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C. Another satellite, the Beidou-2/Compass IGSO-5 satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011. In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million in Galileo over the few years. At the time, it was believed that Chinas BeiDou navigation system would only be used by its armed forces

BeiDou Navigation Satellite System
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The BeiDou system's logo
BeiDou Navigation Satellite System
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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.
BeiDou Navigation Satellite System
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Ground track of BeiDou-M5 (2012-050A)

18.
Compass navigation system
–
The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering services, mainly for customers in China and neighboring regions. It became operational in China in December 2011, with 10 satellites in use and it is planned to begin serving global customers upon its completion in 2020. In-mid 2015, China started the build-up of the third generation BeiDou system in the global coverage constellation, the first BDS-3 satellite was launched 30 September 2015. As of March 2016,4 BDS-3 in-orbit validation satellites have been launched, the official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Běidǒu, the name literally means Northern Dipper, the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris, as such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun, the third satellite, BeiDou-1C, was put into orbit on 25 May 2003. The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system. On 2 November 2006, China announced that from 2008 BeiDou would offer a service with an accuracy of 10 meters, timing of 0.2 microseconds. In February 2007, the fourth and last satellite of the BeiDou-1 system and it was reported that the satellite had suffered from a control system malfunction but was then fully restored. In April 2007, the first satellite of BeiDou-2, namely Compass-M1 was successfully put into its working orbit, the second BeiDou-2 constellation satellite Compass-G2 was launched on 15 April 2009. On 2 June 2010, the satellite was launched successfully into orbit. The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010, three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C. Another satellite, the Beidou-2/Compass IGSO-5 satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011. In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million in Galileo over the few years. At the time, it was believed that Chinas BeiDou navigation system would only be used by its armed forces

Compass navigation system
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The BeiDou system's logo
Compass navigation system
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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.
Compass navigation system
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Ground track of BeiDou-M5 (2012-050A)

19.
India
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India, officially the Republic of India, is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and it is bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast. It shares land borders with Pakistan to the west, China, Nepal, and Bhutan to the northeast, in the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives. Indias Andaman and Nicobar Islands share a border with Thailand. The Indian subcontinent was home to the urban Indus Valley Civilisation of the 3rd millennium BCE, in the following millennium, the oldest scriptures associated with Hinduism began to be composed. Social stratification, based on caste, emerged in the first millennium BCE, early political consolidations took place under the Maurya and Gupta empires, the later peninsular Middle Kingdoms influenced cultures as far as southeast Asia. In the medieval era, Judaism, Zoroastrianism, Christianity, and Islam arrived, much of the north fell to the Delhi sultanate, the south was united under the Vijayanagara Empire. The economy expanded in the 17th century in the Mughal empire, in the mid-18th century, the subcontinent came under British East India Company rule, and in the mid-19th under British crown rule. A nationalist movement emerged in the late 19th century, which later, under Mahatma Gandhi, was noted for nonviolent resistance, in 2015, the Indian economy was the worlds seventh largest by nominal GDP and third largest by purchasing power parity. Following market-based economic reforms in 1991, India became one of the major economies and is considered a newly industrialised country. However, it continues to face the challenges of poverty, corruption, malnutrition, a nuclear weapons state and regional power, it has the third largest standing army in the world and ranks sixth in military expenditure among nations. India is a constitutional republic governed under a parliamentary system. It is a pluralistic, multilingual and multi-ethnic society and is home to a diversity of wildlife in a variety of protected habitats. The name India is derived from Indus, which originates from the Old Persian word Hindu, the latter term stems from the Sanskrit word Sindhu, which was the historical local appellation for the Indus River. The ancient Greeks referred to the Indians as Indoi, which translates as The people of the Indus, the geographical term Bharat, which is recognised by the Constitution of India as an official name for the country, is used by many Indian languages in its variations. Scholars believe it to be named after the Vedic tribe of Bharatas in the second millennium B. C. E and it is also traditionally associated with the rule of the legendary emperor Bharata. Gaṇarājya is the Sanskrit/Hindi term for republic dating back to the ancient times, hindustan is a Persian name for India dating back to the 3rd century B. C. E. It was introduced into India by the Mughals and widely used since then and its meaning varied, referring to a region that encompassed northern India and Pakistan or India in its entirety

20.
France
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France, officially the French Republic, is a country with territory in western Europe and several overseas regions and territories. The European, or metropolitan, area of France extends from the Mediterranean Sea to the English Channel and the North Sea, Overseas France include French Guiana on the South American continent and several island territories in the Atlantic, Pacific and Indian oceans. France spans 643,801 square kilometres and had a population of almost 67 million people as of January 2017. It is a unitary republic with the capital in Paris. Other major urban centres include Marseille, Lyon, Lille, Nice, Toulouse, during the Iron Age, what is now metropolitan France was inhabited by the Gauls, a Celtic people. The area was annexed in 51 BC by Rome, which held Gaul until 486, France emerged as a major European power in the Late Middle Ages, with its victory in the Hundred Years War strengthening state-building and political centralisation. During the Renaissance, French culture flourished and a colonial empire was established. The 16th century was dominated by civil wars between Catholics and Protestants. France became Europes dominant cultural, political, and military power under Louis XIV, in the 19th century Napoleon took power and established the First French Empire, whose subsequent Napoleonic Wars shaped the course of continental Europe. Following the collapse of the Empire, France endured a succession of governments culminating with the establishment of the French Third Republic in 1870. Following liberation in 1944, a Fourth Republic was established and later dissolved in the course of the Algerian War, the Fifth Republic, led by Charles de Gaulle, was formed in 1958 and remains to this day. Algeria and nearly all the colonies became independent in the 1960s with minimal controversy and typically retained close economic. France has long been a centre of art, science. It hosts Europes fourth-largest number of cultural UNESCO World Heritage Sites and receives around 83 million foreign tourists annually, France is a developed country with the worlds sixth-largest economy by nominal GDP and ninth-largest by purchasing power parity. In terms of household wealth, it ranks fourth in the world. France performs well in international rankings of education, health care, life expectancy, France remains a great power in the world, being one of the five permanent members of the United Nations Security Council with the power to veto and an official nuclear-weapon state. It is a member state of the European Union and the Eurozone. It is also a member of the Group of 7, North Atlantic Treaty Organization, Organisation for Economic Co-operation and Development, the World Trade Organization, originally applied to the whole Frankish Empire, the name France comes from the Latin Francia, or country of the Franks

21.
Japan
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Japan is a sovereign island nation in Eastern Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asia Mainland and stretches from the Sea of Okhotsk in the north to the East China Sea, the kanji that make up Japans name mean sun origin. 日 can be read as ni and means sun while 本 can be read as hon, or pon, Japan is often referred to by the famous epithet Land of the Rising Sun in reference to its Japanese name. Japan is an archipelago consisting of about 6,852 islands. The four largest are Honshu, Hokkaido, Kyushu and Shikoku, the country is divided into 47 prefectures in eight regions. Hokkaido being the northernmost prefecture and Okinawa being the southernmost one, the population of 127 million is the worlds tenth largest. Japanese people make up 98. 5% of Japans total population, approximately 9.1 million people live in the city of Tokyo, the capital of Japan. Archaeological research indicates that Japan was inhabited as early as the Upper Paleolithic period, the first written mention of Japan is in Chinese history texts from the 1st century AD. Influence from other regions, mainly China, followed by periods of isolation, from the 12th century until 1868, Japan was ruled by successive feudal military shoguns who ruled in the name of the Emperor. Japan entered into a period of isolation in the early 17th century. The Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the bombings of Hiroshima and Nagasaki. Japan is a member of the UN, the OECD, the G7, the G8, the country has the worlds third-largest economy by nominal GDP and the worlds fourth-largest economy by purchasing power parity. It is also the worlds fourth-largest exporter and fourth-largest importer, although Japan has officially renounced its right to declare war, it maintains a modern military with the worlds eighth-largest military budget, used for self-defense and peacekeeping roles. Japan is a country with a very high standard of living. Its population enjoys the highest life expectancy and the third lowest infant mortality rate in the world, in ancient China, Japan was called Wo 倭. It was mentioned in the third century Chinese historical text Records of the Three Kingdoms in the section for the Wei kingdom, Wa became disliked because it has the connotation of the character 矮, meaning dwarf. The 倭 kanji has been replaced with the homophone Wa, meaning harmony, the Japanese word for Japan is 日本, which is pronounced Nippon or Nihon and literally means the origin of the sun. The earliest record of the name Nihon appears in the Chinese historical records of the Tang dynasty, at the start of the seventh century, a delegation from Japan introduced their country as Nihon

22.
Satellite constellation
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A satellite constellation is a group of artificial satellites working in concert. Many LEO satellites are needed to maintain continuous coverage over an area and this contrasts with geostationary satellites, where a single satellite, moving at the same angular velocity as the rotation of the Earths surface, provides permanent coverage over a large area. A group of formation-flying satellites very close together and moving in almost identical orbits is known as a cluster or Satellite formation flying. There are a number of constellations that may satisfy a particular mission. Usually constellations are designed so that the satellites have similar orbits, eccentricity, in this way, the geometry can be preserved without excessive station-keeping thereby reducing the fuel usage and hence increasing the life of the satellites. Another consideration is that the phasing of each satellite in an orbital plane maintains sufficient separation to avoid collisions or interference at orbit plane intersections, circular orbits are popular, because then the satellite is at a constant altitude requiring a constant strength signal to communicate. A class of circular orbit geometries that has become popular is the Walker Delta Pattern constellation and this has an associated notation to describe it which was proposed by John Walker. The change in true anomaly for equivalent satellites in neighbouring planes is equal to f*360/t, for example, the Galileo Navigation system is a Walker Delta 56°, 27/3/1 constellation. This means there are 27 satellites in 3 planes inclined at 56 degrees, the 1 defines the phasing between the planes, and how they are spaced. The Walker Delta is also known as the Ballard rosette, after A. H. Ballards similar earlier work, Ballards notation is where m is a multiple of the fractional offset between planes. Another popular constellation type is the near-polar Walker Star, which is used by Iridium, here, the satellites are in near-polar circular orbits across approximately 180 degrees, travelling north on one side of the Earth, and south on the other. The active satellites in the full Iridium constellation form a Walker Star of 86. 4°, 66/6/2, Walker uses similar notation for stars and deltas, which can be confusing

Satellite constellation
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The GPS constellation calls for 24 satellites to be distributed equally among six circular orbital planes

23.
Medium Earth orbit
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Medium Earth orbit, sometimes called intermediate circular orbit, is the region of space around the Earth above low Earth orbit and below geostationary orbit. The most common use for satellites in this region is for navigation, communication, the most common altitude is approximately 20,200 kilometres ), which yields an orbital period of 12 hours, as used, for example, by the Global Positioning System. Other satellites in medium Earth orbit include Glonass and Galileo constellations, communications satellites that cover the North and South Pole are also put in MEO. The orbital periods of MEO satellites range from about 2 to nearly 24 hours, telstar 1, an experimental satellite launched in 1962, orbits in MEO. The orbit is home to a number of artificial satellites

24.
Orbital inclination
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Orbital inclination measures the tilt of an objects orbit around a celestial body. It is expressed as the angle between a plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the orbit is the same as the Earths equatorial plane. The general case is that the orbit is tilted, it spends half an orbit over the northern hemisphere. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°, the inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the plane and the plane of reference, normally stated in degrees. For a satellite orbiting a planet, the plane of reference is usually the plane containing the planets equator, for planets in the Solar System, the plane of reference is usually the ecliptic, the plane in which the Earth orbits the Sun. This reference plane is most practical for Earth-based observers, therefore, Earths inclination is, by definition, zero. Inclination could instead be measured with respect to another plane, such as the Suns equator or the invariable plane, the inclination of orbits of natural or artificial satellites is measured relative to the equatorial plane of the body they orbit, if they orbit sufficiently closely. The equatorial plane is the perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°, the convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits, thus, An inclination of 0° means the orbiting body has a prograde orbit in the planets equatorial plane. An inclination greater than 0° and less than 90° also describe prograde orbits, an inclination of 63. 4° is often called a critical inclination, when describing artificial satellites orbiting the Earth, because they have zero apogee drift. An inclination of exactly 90° is an orbit, in which the spacecraft passes over the north and south poles of the planet. An inclination greater than 90° and less than 180° is a retrograde orbit, an inclination of exactly 180° is a retrograde equatorial orbit. For gas giants, the orbits of moons tend to be aligned with the giant planets equator, the inclination of exoplanets or members of multiple stars is the angle of the plane of the orbit relative to the plane perpendicular to the line-of-sight from Earth to the object. An inclination of 0° is an orbit, meaning the plane of its orbit is parallel to the sky. An inclination of 90° is an orbit, meaning the plane of its orbit is perpendicular to the sky

Orbital inclination
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Fig. 1: One view of inclination i (green) and other orbital parameters

25.
Satellite Based Augmentation System
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There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information. A satellite-based augmentation system is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages, such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users. SBAS is sometimes synonymous with WADGPS, wide-area DGPS, for details on how various SBAS are implemented, please see the following articles, The Wide Area Augmentation System, operated by the United States Federal Aviation Administration. The European Geostationary Navigation Overlay Service, operated by the ESSP, the Multi-functional Satellite Augmentation System system, operated by Japans Ministry of Land, Infrastructure and Transport Japan Civil Aviation Bureau. The Quasi-Zenith Satellite System, proposed by Japan, the GPS Aided Geo Augmented Navigation system being operated by India. The GLONASS System for Differential Correction and Monitoring, proposed by Russia, the Satellite Navigation Augmentation System, proposed by China. The Wide Area GPS Enhancement, operated by the United States Department of Defense for use by military, the commercial StarFire navigation system, operated by John Deere and C-Nav Positioning Solutions. Each of the terms ground-based augmentation system and ground-based regional augmentation system describe a system that supports augmentation through the use of radio messages. Generally, GBAS is localized, supporting receivers within 23 nautical miles, the shorter the distance between the ground station that calculates the differential corrections to the inbound plane, the higher the accuracy is likely to be. International Civil Aviation Organization Ground-Based Augmentation System applies to precision landing of civil aircraft. Originally this system was called the Local Area Augmentation System The US Nationwide Differential GPS System, An augmentation system for users on U. S. land and waterways. See also, the Differential GPS Wikipedia page The augmentation may also take the form of information being blended into the position calculation. Many times the additional avionics operate via separate principles than the GNSS and are not necessarily subject to the sources of error or interference. A system such as this is referred to as an aircraft-based augmentation system by the ICAO. net lists all GLS sites worldwide

Satellite Based Augmentation System
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Service areas of satellite-based augmentation systems (SBAS).

26.
Ground Based Augmentation System
–
There are many such systems in place and they are generally named or described based on how the GNSS sensor receives the external information. A satellite-based augmentation system is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages, such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users. SBAS is sometimes synonymous with WADGPS, wide-area DGPS, for details on how various SBAS are implemented, please see the following articles, The Wide Area Augmentation System, operated by the United States Federal Aviation Administration. The European Geostationary Navigation Overlay Service, operated by the ESSP, the Multi-functional Satellite Augmentation System system, operated by Japans Ministry of Land, Infrastructure and Transport Japan Civil Aviation Bureau. The Quasi-Zenith Satellite System, proposed by Japan, the GPS Aided Geo Augmented Navigation system being operated by India. The GLONASS System for Differential Correction and Monitoring, proposed by Russia, the Satellite Navigation Augmentation System, proposed by China. The Wide Area GPS Enhancement, operated by the United States Department of Defense for use by military, the commercial StarFire navigation system, operated by John Deere and C-Nav Positioning Solutions. Each of the terms ground-based augmentation system and ground-based regional augmentation system describe a system that supports augmentation through the use of radio messages. Generally, GBAS is localized, supporting receivers within 23 nautical miles, the shorter the distance between the ground station that calculates the differential corrections to the inbound plane, the higher the accuracy is likely to be. International Civil Aviation Organization Ground-Based Augmentation System applies to precision landing of civil aircraft. Originally this system was called the Local Area Augmentation System The US Nationwide Differential GPS System, An augmentation system for users on U. S. land and waterways. See also, the Differential GPS Wikipedia page The augmentation may also take the form of information being blended into the position calculation. Many times the additional avionics operate via separate principles than the GNSS and are not necessarily subject to the sources of error or interference. A system such as this is referred to as an aircraft-based augmentation system by the ICAO. net lists all GLS sites worldwide

Ground Based Augmentation System
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Service areas of satellite-based augmentation systems (SBAS).

27.
Wide Area Augmentation System
–
Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area. It may be enhanced with the Local Area Augmentation System in critical areas. WAAS uses a network of ground-based reference stations, in North America and Hawaii and those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy. The International Civil Aviation Organization calls this type of system a satellite-based augmentation system, commercial systems include StarFire and OmniSTAR. The WAAS specification requires it to provide an accuracy of 7.6 metres or less. With these results, WAAS is capable of achieving the required Category I precision approach accuracy of 16 metres laterally and 4.0 metres vertically, Integrity of a navigation system includes the ability to provide timely warnings when its signal is providing misleading data that could potentially create hazards. The WAAS specification requires the system detect errors in the GPS or WAAS network, certifying that WAAS is safe for instrument flight rules requires proving there is only an extremely small probability that an error exceeding the requirements for accuracy will go undetected. Specifically, the probability is stated as 1×10−7, and is equivalent to no more than 3 seconds of bad data per year and this provides integrity information equivalent to or better than Receiver Autonomous Integrity Monitoring. Availability is the probability that a system meets the accuracy. Before the advent of WAAS, GPS specifications allowed for system unavailability for as much as a time of four days per year. The WAAS specification mandates availability as 99. 999% throughout the service area, as with GPS in general, WAAS is composed of three main segments, the ground segment, space segment, and user segment. The ground segment is composed of multiple Wide-area Reference Stations and these precisely surveyed ground stations monitor and collect information on the GPS signals, then send their data to three Wide-area Master Stations using a terrestrial communications network. The reference stations also monitor signals from WAAS geostationary satellites, providing integrity information regarding them as well. As of October 2007 there were 38 WRSs, twenty in the contiguous United States, seven in Alaska, one in Hawaii, one in Puerto Rico, five in Mexico, and four in Canada. Using the data from the WRS sites, the WMSs generate two different sets of corrections, fast and slow, the fast corrections are for errors which are changing rapidly and primarily concern the GPS satellites instantaneous positions and clock errors. These corrections are considered user position-independent, which means they can be applied instantly by any receiver inside the WAAS broadcast footprint, the slow corrections include long-term ephemeric and clock error estimates, as well as ionospheric delay information. WAAS supplies delay corrections for a number of points across the WAAS service area, once these correction messages are generated, the WMSs send them to two pairs of Ground Uplink Stations, which then transmit to satellites in the Space segment for rebroadcast to the User segment. Each FAA Air Route Traffic Control Center in the 50 states has a WAAS reference station, there are also stations positioned in Canada, Mexico and Puerto Rico

Wide Area Augmentation System
–
WAAS system overview
Wide Area Augmentation System
–
WAAS reference station in Barrow, Alaska
Wide Area Augmentation System
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WAAS ground uplink station (GUS) in Napa, California

28.
European Geostationary Navigation Overlay Service
–
The European Geostationary Navigation Overlay Service is a satellite based augmentation system developed by the European Space Agency, the European Commission and EUROCONTROL. It supplements the GPS, GLONASS and Galileo satellite navigation systems by reporting on the reliability and accuracy of their positioning data, EGNOS consists of a network of about 40 ground stations and 3 geostationary satellites. One main use of the system is in aviation, according to specifications, horizontal position accuracy when using EGNOS-provided corrections should be better than seven metres. In practice, the position accuracy is at the metre level. Similar service is provided in North America by the Wide Area Augmentation System, the system started its initial operations in July 2005, with accuracy better than two metres and availability above 99%. As of July 2005, EGNOS has been broadcasting a continuous signal, in 2009, the European Commission announced it had signed a contract with the company European Satellite Services Provider to run EGNOS. The official start of operations was announced by the European Commission on 1 October 2009, the system was certified for use in safety of life applications in March 2011. An EGNOS Data Access Service became available in July 2012, initial work to extend EGNOS coverage to the Southern Africa region is being done under a project called ESESA - EGNOS Service Extension to South Africa. The European Commission is defining the roadmap for the evolution of the EGNOS mission and this roadmap should cope with legacy and new missions, 2011-2030, En-route / NPA / APV1 / LPV200 service based on augmentation of GPS L1 only. The Safety Of Life will be guaranteed up to 2030 in compliance with ICAO SBAS SARPS, similar to WAAS, EGNOS is mostly designed for aviation users who enjoy unperturbed reception of direct signals from geostationary satellites up to very high latitudes. To address this problem, ESA released in 2002 SISNeT, an Internet service designed for delivery of EGNOS signals to ground users. The first experimental SISNeT receiver was created by the Finnish Geodetic Institute, the commercial SISNeT receivers have been developed by Septentrio. In March 2011, the EGNOS Safety of Live Service was deemed acceptable for use in aviation and this allows pilots throughout Europe to use the EGNOS system as a form of positioning during an approach, and allows pilots to land the aircraft in IMC using a GPS approach. As of September 2014 LPV landing procedures, which are EGNOS-enabled, were available at more than 114 airports across Europe

European Geostationary Navigation Overlay Service
–
EGNOS RIMS "BRN" (Berlin) close to Berlin
European Geostationary Navigation Overlay Service
–
Map of the EGNOS ground network

29.
Multi-Functional Transport Satellite
–
Multifunctional Transport Satellites are a series of weather and aviation control satellites. They replace the GMS-5 satellite, also known as Himawari 5 and they can provide imagery in five wavelength bands — visible and four infrared, including the water vapour channel. The visible light camera has a resolution of 1 km, the cameras have 4 km. The spacecraft have a lifespan of five years. MTSAT-1 and 1R were built by Space Systems/Loral and it was replaced by Himawari 8 on 7 July 2015. The launch of MTSAT-1, on a Japanese H-II rocket, failed on November 15,1999, GMS-5, the satellite MTSAT-1 was intended to replace, was decommissioned on April 1,2003 leaving Japan without weather satellite imagery. To fill in the void, The United States National Oceanic and Atmospheric Administration loaned the GOES-9 satellite to the JMA, GOES-9 was decommissioned when MTSAT-1R came online in June 2005. Its solar sail counteracts the torque produced by pressure on the solar array. The trim tab on the solar array makes small adjustments to the torque balance, MTSAT-1R was decommissioned on December 4,2015, due to fuel limitations. MTSAT-2 successfully launched on February 18,2006 and is positioned at 145° East, the weather functions of MTSAT-2 were put into hibernation until the end of MTSAT-1R’s life. The transportation and communication functions of MTSAT-2 will be utilized prior to that time, on November 5,2007 JMA announced a malfunction in the attitude control of MTSAT-2. Attitude control was restored November 7,2007, the presumed cause of the malfunction was improper functioning of an attitude control thruster. A spare thruster was used to return the spacecraft to normal operation, ground stations for both satellites are located in Kobe and Hitachiota, Japan. Online MTSAT weather satellite viewer with 2 months of archived data

Multi-Functional Transport Satellite
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MTSAT-1 Himawari 6

30.
Local Area Augmentation System
–
The Local Area Augmentation System is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a location at the airport. This data is used to formulate a message, which is then transmitted to users via a VHF Data Link. A receiver on an aircraft uses this information to correct GPS signals, the FAA has stopped using the term LAAS and has transitioned to the International Civil Aviation Organization terminology of Ground Based Augmentation System. The FAA has indefinitely delayed plans for federal GBAS acquisition, the system can be purchased by airports, the history of these standards can trace back to efforts in the United States by the Federal Aviation Administration to developed a Local Area Augmentation System. Many references still refer to LAAS, although the current international terminology is GBAS and GBAS Landing System, GBAS monitors GNSS satellites and provides correction messages to users in the vicinity of the GBAS station. The monitoring enables the GBAS to detect anomalous GPS satellite behavior, the GBAS provides corrections to the GPS signals with a resulting improvement in accuracy sufficient to support aircraft precision approach operations. For more information on how GBAS works, see GBAS-How It Works, current GBAS standards only augment a single GNSS frequency and support landings to Category-1 minima. These GBAS systems are identified as GBAS Approach Service Type C, draft requirements for a GAST-D system are under review by ICAO. A GAST-D system will support operations to Category-III minima, many organizations are conducting research in multi-frequency GBAS. Other efforts are exploring the addition of Galileo corrections for GBAS, Honeywell has developed a Non-Federal CAT-1 GBAS which received System Design Approval from the Federal Aviation Administration in September 2009. The GBAS installation at Newark Liberty International Airport achieved Operational Approval on Sept.28,2012, a second GBAS installed at Houston Intercontinental Airport received Operational Approval on April 23,2013. Honeywell systems are installed internationally, with an operational system in Bremen. Additional systems are installed or in the process of being installed, Operational approval of several more systems is expected shortly. Local reference receivers are located around an airport at precisely surveyed locations, the signal received from the GPS constellation is used to calculate the position of the LAAS ground station, which is then compared to its precisely surveyed position. This data is used to formulate a message which is transmitted to users via a VHF data link. A receiver on the aircraft uses this information to correct the GPS signals it receives and this information is used to create an ILS-type display for aircraft approach and landing purposes. Honeywell’s CAT I system provides precision approach service within a radius of 23 NM surrounding a single airport, LAAS mitigates GPS threats in the Local Area to a much greater accuracy than WAAS and therefore provides a higher level of service not attainable by WAAS

Local Area Augmentation System
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LAAS Architecture

31.
StarFire (navigation system)
–
StarFire is a wide-area differential GPS developed by John Deeres NavCom and precision farming groups.5 cm. StarFire is similar to the FAAs differential GPS Wide Area Augmentation System, StarFire came about after a meeting in 1994 among John Deere engineers who were attempting to chart a course for future developments. At the time, a number of companies were attempting to introduce yield-mapping systems combining a GPS receiver with a grain counter. The engineers felt this was one of the most interesting developments in the industry, the various providers went bankrupt over the next few years. In 1997, a team was formed to solve the problem of providing a more accurate GPS fix, along with members of John Deeres engineering team, a small project at Stanford University also took part, along with NASA engineers at the Jet Propulsion Laboratory. They decided to produce a system that differed fairly dramatically from similar systems like WAAS. In theory the GPS signal with Selective Availability turned off offers accuracy on the order of 3 m, in practice, typical accuracy is about 15 m. Of this 12 m, about 5 m is due to distortion from billows in the ionosphere, DGPS correct for these errors by comparing the position measured using GPS with a known highly accurate ground reference, and then calculating the difference and broadcasting it to users. Some of these apply to any location - the corrections to the clocks. In contrast, the cover only a certain portion of the sky. To make the corrections accurate over an area, one would need to deploy many ground reference stations. For instance, WAAS uses twenty-five stations in the continental US, StarFire instead uses an advanced receiver to correct for ionospheric effects internally. To do this, it captures the P signal that is broadcast on two frequencies, L1 and L2, and compares the effects of the ionosphere on the time of the two. Using this information, the effects can be calculated to a very high degree of accuracy. The second P signal is encrypted and cannot be used by civilian receivers directly and this is expensive in terms of electronics, requiring a second tuner and excellent signal stability to be useful, which is why the StarFire-like solution is not more widely used. Since these corrections are globally valid, and there are only 24 satellites in operation at any time, StarFire broadcasts this data at 300 bits per second, repeating once a second. The corrections are generally valid for about 20 minutes, StarFire has developed through two versions. The first, retroactively known as SF1, offered 1-sigma accuracy of about 1 m and its error was about 15 to 30 cm, meaning that while the displayed position might be off by about 1 m, it could return you to within centimeters of a previously measured spot

32.
GPS-aided geo-augmented navigation
–
The GPS Aided GEO Augmented Navigation is an implementation of a regional satellite-based augmentation system by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals and it will be able to help pilots to navigate in the Indian airspace by an accuracy of 3 m. This will be helpful for landing aircraft in weather and terrain like Mangalore. The ₹7.74 billion project is being created in three phases through 2008 by the Airport Authority of India with the help of the Indian Space Research Organizations technology and space support. The goal is to provide navigation system for all phases of flight over the Indian airspace and it is applicable to safety-to-life operations, and meets the performance requirements of international civil aviation regulatory bodies. The space component will become available after the GAGAN payload on the GSAT-8 communication satellite and this payload was also on the GSAT-4 satellite that was lost when the Geosynchronous Satellite Launch Vehicle failed during launch in April 2010. Final System Acceptance Test was conducted during June 2012 followed by system certification during July 2013. S Department of Defense on November 2001 and March 2005. The system will use eight reference stations located in Delhi, Guwahati, Kolkata, Ahmedabad, Thiruvananthapuram, Bangalore, Jammu and Port Blair, US defense contractor Raytheon has stated they will bid to build the system. TDS was successfully completed during 2007 by installing eight Indian Reference Stations at eight Indian airports, preliminary System Acceptance Testing has been successfully completed in December 2010. The ground segment for GAGAN, which has put up by the Raytheon, has 15 reference stations scattered across the country. Two mission control centres, along with associated uplink stations, have set up at Kundalahalli in Bangalore. One more control centre and uplink station are to come up at Delhi, gAGANs TDS signal in space provides a three-metre accuracy as against the requirement of 7.6 metres. Flight inspection of GAGAN signal is being carried out at Kozhikode, Hyderabad, Nagpur and Bangalore airports, one essential component of the GAGAN project is the study of the ionospheric behavior over the Indian region. This has been taken up in view of the rather uncertain nature of the behavior of the ionosphere in the region. The study will lead to the optimization of the algorithms for the corrections in the region. The space segment will consist of one geo-navigation transponder, a flight-management system based on GAGAN will then be poised to save operators time and money by managing climb, descent and engine performance profiles. The FMS will improve the efficiency and flexibility by increasing the use of operator-preferred trajectories and it will improve airport and airspace access in all weather conditions, and the ability to meet the environmental and obstacle clearance constraints. It will also enhance reliability and reduce delays by defining more precise terminal area procedures that feature parallel routes, GAGAN will also offer high position accuracies over a wide geographical area like the Indian airspace

GPS-aided geo-augmented navigation
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Organisations

33.
Beidou navigation system
–
The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering services, mainly for customers in China and neighboring regions. It became operational in China in December 2011, with 10 satellites in use and it is planned to begin serving global customers upon its completion in 2020. In-mid 2015, China started the build-up of the third generation BeiDou system in the global coverage constellation, the first BDS-3 satellite was launched 30 September 2015. As of March 2016,4 BDS-3 in-orbit validation satellites have been launched, the official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Běidǒu, the name literally means Northern Dipper, the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris, as such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun, the third satellite, BeiDou-1C, was put into orbit on 25 May 2003. The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system. On 2 November 2006, China announced that from 2008 BeiDou would offer a service with an accuracy of 10 meters, timing of 0.2 microseconds. In February 2007, the fourth and last satellite of the BeiDou-1 system and it was reported that the satellite had suffered from a control system malfunction but was then fully restored. In April 2007, the first satellite of BeiDou-2, namely Compass-M1 was successfully put into its working orbit, the second BeiDou-2 constellation satellite Compass-G2 was launched on 15 April 2009. On 2 June 2010, the satellite was launched successfully into orbit. The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010, three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C. Another satellite, the Beidou-2/Compass IGSO-5 satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011. In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million in Galileo over the few years. At the time, it was believed that Chinas BeiDou navigation system would only be used by its armed forces

Beidou navigation system
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The BeiDou system's logo
Beidou navigation system
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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.
Beidou navigation system
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Ground track of BeiDou-M5 (2012-050A)

34.
Indian Regional Navigation Satellite System
–
The Indian government approved the project in May 2006. The constellation of seven NAVIC satellites is already in orbit and the system is expected to be operational from September 2016, NAVIC will provide two levels of service, the standard positioning service will be open for civilian use, and a restricted service for authorized users. As part of the project, the Indian Space Research Organisation opened a new satellite navigation center within the campus of ISRO Deep Space Network at Byalalu, in Karnataka on 28 May 2013. A network of 21 ranging stations located across the country will provide data for the determination of the satellites. A goal of complete Indian control has been stated, with the segment, ground segment. Its location in low latitudes facilitates a coverage with low-inclination satellites, three satellites will be in geostationary orbit over the Indian Ocean. Missile targeting could be an important military application for the constellation, the total cost of the project is expected to be ₹1,420 crore, with the cost of the ground segment being ₹300 crore. Each satellites costing ₹150 crore and the PSLV-XL version rocket costs around ₹130 crore, the seven rockets would involve an outlay of around ₹910 crore. The NAVIC signal was released for evaluation in September 2014, in April 2010, it was reported that India plans to start launching satellites by the end of 2011, at a rate of one satellite every six months. This would have made NAVIC functional by 2015, but the program was delayed, and India also launched 3 new satellites to supplement this. Seven satellites with the prefix IRNSS-1 will constitute the space segment of the IRNSS, IRNSS-1A, the first of the seven satellites, was launched on 1 July 2013. IRNSS-1B was launched on 4 April 2014 on board the PSLV-C24 rocket, the satellite has been placed in geosynchronous orbit. IRNSS-1C was launched on 16 October 2014, IRNSS-1D on 28 March 2015, IRNSS-1E on 20 January 2016, IRNSS-1F on 10 March 2016, the system consists of a constellation of seven satellites and a support ground segment. Three of the satellites in the constellation are located in orbit at 32. 5° East, 83° East. The other four are inclined geosynchronous orbit, two of the GSOs cross the equator at 55° East and two at 111. 75° East. The four GSO satellites will appear to be moving in the form of an 8, in addition, various ground-based systems will control, track orbits, check integration and send radio signals to the satellites. The land-based Master Control Center will run navigational software, NAVIC signals will consist of a Standard Positioning Service and a Precision Service. Both will be carried on L5 and S band, the SPS signal will be modulated by a 1 MHz BPSK signal

35.
QZSS
–
The first satellite Michibiki was launched on 11 September 2010. Full operational status was expected by 2013, in March 2013, Japans Cabinet Office announced the expansion of the Quasi-Zenith Satellite System from three satellites to four. The $526 million contract with Mitsubishi Electric for the construction of three satellites is slated for launch before the end of 2017, the basic four-satellite system is planned to be operational in 2018. The work was taken over by the Satellite Positioning Research and Application Center, QZSS is targeted at mobile applications, to provide communications-based services and positioning information. With regards to its service, QZSS can only provide limited accuracy on its own and is not currently required in its specifications to work in a stand-alone mode. As such, it is viewed as a GNSS Augmentation service. S, federal Aviation Administrations Wide Area Augmentation System. QZSS uses three satellites, each 120° apart, in highly inclined, slightly elliptical, geosynchronous orbits, because of this inclination, they are not geostationary, they do not remain in the same place in the sky. Instead, their ground traces are asymmetrical figure-8 patterns, designed to ensure one is almost directly overhead over Japan at all times. The nominal orbital elements are, The primary purpose of QZSS is to increase the availability of GPS in Japans numerous urban canyons, a secondary function is performance enhancement, increasing the accuracy and reliability of GPS derived navigation solutions. The Quasi-Zenith Satellites transmit signals compatible with the GPS L1C/A signal, as well as the modernized GPS L1C, L2C signal and this minimizes changes to existing GPS receivers. It also improves reliability by means of monitoring and system health data notifications. QZSS also provides other support data to users to improve GPS satellite acquisition, according to its original plan, QZSS was to carry two types of space-borne atomic clocks, a hydrogen maser and a rubidium atomic clock. The development of a hydrogen maser for QZSS was abandoned in 2006. The positioning signal will be generated by a Rb clock and a similar to the GPS timekeeping system will be employed. Although the ﬁrst generation QZSS timekeeping system will be based on the Rb clock, during the ﬁrst half of the two year in-orbit test phase, preliminary tests will investigate the feasibility of the atomic clock-less technology which might be employed in the second generation QZSS. This allows the system to operate optimally when satellites are in contact with the ground station. Low satellite mass and low satellite manufacturing and launch cost are significant advantages of this system

QZSS
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Quasi-Zenith satellite orbit

36.
Differential GPS
–
DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the GPS satellite systems and the known fixed positions. These stations broadcast the difference between the measured satellite pseudoranges and actual pseudoranges, and receiver stations may correct their pseudoranges by the same amount, the digital correction signal is typically broadcast locally over ground-based transmitters of shorter range. The term refers to a technique of augmentation. The United States Coast Guard and Canadian Coast Guard each run such systems in the U. S. the USCGs DGPS system has been named NDGPS and is now jointly administered by the Coast Guard and the U. S. Department of Transportation’s Federal Highway Administration. It consists of broadcast sites located throughout the inland and coastal portions of the United States including Alaska, Hawaii, a similar system that transmits corrections from orbiting satellites instead of ground-based transmitters is called a Wide-Area DGPS or Satellite Based Augmentation System. When GPS was first being put into service, the US military was concerned about the possibility of enemy forces using the globally available GPS signals to guide their own weapon systems. Originally, the government thought the coarse acquisition signal would only give about 100 meter accuracy, but with improved receiver designs and this technique, known as Selective Availability, or SA for short, seriously degraded the usefulness of the GPS signal for non-military users. This presented a problem for users who relied upon ground-based radio navigation systems such as LORAN, VOR. The advent of a global satellite system could provide greatly improved accuracy. The accuracy inherent in the S/A signal was too poor to make this realistic. Through the early to mid 1980s, a number of developed a solution to the SA problem. This suggested that broadcasting this offset to local GPS receivers could eliminate the effects of SA, resulting in closer to GPSs theoretical performance. Additionally, another source of errors in a GPS fix is due to transmission delays in the ionosphere. This offered an improvement to about 5 meters accuracy, more than enough for most civilian needs, the US Coast Guard was one of the more aggressive proponents of the DGPS system, experimenting with the system on an ever-wider basis through the late 1980s and early 1990s. These signals are broadcast on marine longwave frequencies, which could be received on existing radiotelephones, almost all major GPS vendors offered units with DGPS inputs, not only for the USCG signals, but also aviation units on either VHF or commercial AM radio bands. Plans were put into place to expand the system across the US, the quality of the DGPS corrections generally fell with distance, and large transmitters capable of covering large areas tend to cluster near cities. This meant that lower-population areas, notably in the midwest and Alaska, in addition the system provides single or dual coverage to a majority of the inland portion of United States. Instead, the FAA started studying broadcasting the signals across the entire hemisphere from communications satellites in geostationary orbit and this led to the Wide Area Augmentation System and similar systems, although these are generally not referred to as DGPS, or alternatively, wide-area DGPS

37.
Real Time Kinematic
–
Real Time Kinematic satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems such as GPS, GLONASS, Galileo, and BeiDou. With reference to GPS in particular, the system is referred to as Carrier-Phase Enhancement. It has applications in land survey, hydrographic survey, and in consumer Unmanned aerial vehicle navigation, normally, satellite navigation receivers must align signals sent from the satellite to an internally generated version of a pseudorandom binary sequence, also contained in the signal. Since the satellite signal takes time to reach the receiver, the two sequences do not initially coincide, the copy is delayed in relation to the local copy. By increasingly delaying the local copy, the two copies can eventually be aligned, the correct delay represents the time needed for the signal to reach the receiver, and from this the distance from the satellite can be calculated. RTK follows the general concept, but uses the satellite signals carrier wave as its signal. The improvement possible using this signal is very high if one continues to assume a 1% accuracy in locking. For instance, in the case of GPS, the coarse-acquisition code changes phase at 1.023 MHz, but the L1 carrier itself is 1575.42 MHz, the carrier frequency corresponds to a wavelength of 19 cm for the L1 signal. A ±1% error in L1 carrier phase measurement thus corresponds to a ±1.9 mm error in baseline estimation, the difficulty in making an RTK system is properly aligning the signals. The navigation signals are encoded in order to allow them to be aligned easily. This makes it difficult to know if you have properly aligned the signals or if they are off by one and are thus introducing an error of 19 cm. However, none of these methods can reduce this error to zero, in practice, RTK systems use a single base station receiver and a number of mobile units. The base station re-broadcasts the phase of the carrier that it observes, there are several ways to transmit a correction signal from base station to mobile station. The most popular way to achieve real-time, low-cost signal transmission is to use a radio modem, in most countries, certain frequencies are allocated specifically for RTK purposes. Most land survey equipment has a built-in UHF band radio modem as a standard option and this allows the units to calculate their relative position to within millimeters, although their absolute position is accurate only to the same accuracy as the computed position of the base station. The typical nominal accuracy for these systems is 1 centimetre ±2 parts-per-million horizontally and 2 centimetres ±2 ppm vertically, although these parameters limit the usefulness of the RTK technique for general navigation, the technique is perfectly suited to roles like surveying. In this case, the station is located at a known surveyed location, often a benchmark. RTK has also found uses in autodrive/autopilot systems, precision farming, machine control systems, the Virtual Reference Station method extends the use of RTK to a whole area of a reference station network

Real Time Kinematic
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North SmaRTK GNSS RTK Receiver being used to survey the forest population in Switzerland.

38.
Radio navigation
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Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth. Like radiolocation, it is a type of radiodetermination and these systems used some form of directional radio antenna to determine the location of a broadcast station on the ground. Conventional navigation techniques are used to take a radio fix. These were introduced prior to World War I, and remain in use today, the first system of radio navigation was the Radio Direction Finder, or RDF. By tuning in a station and then using a directional antenna. A second measurement using another station was then taken, using triangulation, the two directions can be plotted on a map where their intersection reveals the location of the navigator. Early RDF systems normally used an antenna, a small loop of metal wire that is mounted so it can be rotated around a vertical axis. By rotating the loop and looking for the angle of the null, loop antennas can be seen on most pre-1950s aircraft and ships. The main problem with RDF is that it required a special antenna on the vehicle, a smaller problem is that the accuracy of the system is based to a degree on the size of the antenna, but larger antennas would likewise make the installation more difficult. During the era between World War I and World War II, a number of systems were introduced that placed the antenna on the ground. Then they waited for the signal to either peak or disappear as the antenna pointed in their direction. By timing the delay between the signal and the peak/null, then dividing by the known rotational rate of the station. The first such system was the German Telefunken Kompass Sender, which operations in 1907 and was used operationally by the Zeppelin fleet until 1918. An improved version was introduced by the UK as the Orfordness Beacon in 1929, a number of improved versions followed, replacing the mechanical motion of the antennas with phasing techniques that produced the same output pattern with no moving parts. One of the longest lasting examples was Sonne, which went into operation just before World War II, the modern VOR system is based on the same principles. A great advance in the RDF technique was introduced in the form of phase comparisons of a signal as measured on two or more antennas, or a single highly directional solenoid. These receivers were dramatically smaller, more accurate, and simpler to operate and this also led to a revival in the operation of simple radio beacons for use with these RDF systems, now referred to as non-directional beacons. As the LF/MF signals used by NDBs can follow the curvature of earth, NDB can be categorized as long range or short range depending on their power

Radio navigation
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Amelia Earhart 's Lockheed Electra had a prominent RDF loop on the cockpit roof.
Radio navigation
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This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2013)
Radio navigation
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The Orfordness Beacon as it appears today.
Radio navigation
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VOR transmitter station

39.
Decca Navigator System
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The Decca Navigator System was a hyperbolic radio navigation system which allowed ships and aircraft to determine their position by receiving radio signals from fixed navigational beacons. The system used phase comparison of low frequencies from 70 to 129 kHz, as opposed to pulse timing systems like Gee and this made it much easier to implement the receivers using 1940s electronics. The system was invented in the US, but development was carried out by Decca in the UK, after the war it was extensively developed around the UK and later used in many areas around the world. Deccas primary use was for ship navigation in coastal waters, offering much better accuracy than the competing LORAN system, fishing vessels were major post-war users, but it was also used on aircraft, including a very early application of moving map displays. The system was deployed extensively in the North Sea and was used by helicopters operating to oil platforms, the opening of the more accurate Loran-C system to civilian use in 1974 offered stiff competition, but Decca was well established by this time and continued operations into the 1990s. Decca was eventually replaced, along with Loran and other similar systems, the Decca system in Europe was shut down in the spring of 2000, and the last worldwide chain, in Japan, in 2001. The Decca Navigator System consisted of a number of land-based radio beacons organised into chains, each chain consisted of a master station and three slave stations, termed Red, Green and Purple. Ideally, the slaves would be positioned at the vertices of a triangle with the master at the centre. The baseline length, that is, the distance, was typically 60–120 nautical miles. As there were three Slaves there were three patterns, termed Red, Green and Purple, the patterns were drawn on nautical charts as a set of hyperbolic lines in the appropriate colour. When two stations transmit at the frequency, the difference in phase between the two signals is constant along a hyperbolic path. The interval between two adjacent hyperbolas on which the signals are in phase was called a lane, other receivers, typically for aeronautical applications, divided the transmitted frequencies down to the basic frequency for phase comparison, rather than multiplying them up to the LCM frequency. Early Decca receivers were fitted with three rotating Decometers that indicated the difference for each pattern. Each Decometer drove a second indicator that counted the number of lanes traversed – each 360 degrees of difference was one lane traversed. In this way, assuming the point of departure was known, the lanes were grouped into zones, with 18 green,24 red, or 30 purple lanes in each zone. This meant that on the baseline the zone width was the same for all three patterns of a given chain. Typical lane and zone widths on the baseline are shown in the table below, the zones were labelled A to J, repeating after J. A Decca position coordinate could thus be written, Red I16.30, later receivers incorporated a microprocessor and displayed a position in latitude and longitude

Decca Navigator System
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The display head, or "decometer bowl", of a Decca Navigator Mk 12 (ca. 1962). Not shown is the much larger receiver unit.
Decca Navigator System
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This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2011)
Decca Navigator System
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An ap Decca receiver Mk II from the 1980s which could be purchased instead of leased. It could store 25 waypoints.

40.
GEE
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Gee, sometimes written GEE, was a radio navigation system used by the Royal Air Force during World War II. It measured the time delay between two signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up to about 350 miles. It was the first hyperbolic system to be used operationally. For large, fixed targets, like the cities that were attacked at night, jamming reduced its usefulness as a bombing aid, but it remained in use as a navigational aid in the UK area throughout the war. Gee remained an important part of the Royal Air Forces suite of systems in the post-war era, and was featured on aircraft such as the English Electric Canberra. It also saw use, and a number of new Gee chains were set up to support military. The system started to be shut down in the late 1960s, Gee also inspired the original LORAN system The basic idea of radio-based hyperbolic navigation was well known in the 1930s, but the equipment needed to build it was not widely available at the time. The main problem involved the determination of the difference in timing of two closely spaced signals, differences in milli- and micro-seconds. During the 1930s, the development of radar demanded devices that could measure these sorts of signal timings. In the case of Chain Home, transmission aerials sent out signals, an oscilloscope was used to measure the time between transmission and reception. The transmitter triggered a trace moving quickly along the oscilloscope display, Radar can also be used as a navigation system. If two stations are able to communicate, they could compare their measurements of the distance to a target and this calculation could then be sent to the aircraft by radio. This is a fairly manpower-intensive operation, and while it was used by both the British and Germans during the war, the workload meant it could only be used to guide single aircraft. In October 1937, Robert J. Dippy, working at Robert Watson-Watts radar laboratory at RAF Bawdsey and he envisaged two transmitting antennas positioned about 10 miles apart on either side of a runway. A transmitter midway between the two antennas would send a signal to both, which would ensure that both antennas would re-broadcast the signal at the same instant. A receiver in the aircraft would tune in these signals and send them to an A-scope type display, if the aircraft was properly lined up with the runway, both signals would be received at the same instant, and thus be drawn at the same point on the display. If the aircraft was located to one side or the other, one of the signals would be received before the other, forming two distinct peaks on the display. By determining which signal was being received first, pilots would know that they were closer to that antenna, watt liked the idea, but at the time there did not appear to be a pressing need for the system

GEE
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GEE airborne equipment, with the R1355 receiver on the left and the Indicator Unit Type 62A on the right. The 'scope shows a simulated display, including the "ghost" A1 signal.
GEE
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GEE control bays
GEE
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GEE transmitter
GEE
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Low-level photo of a light mobile Gee station operating in a field near Roermond, Holland. These forward stations provided Gee coverage deeper into Germany, as well as strong signals for aircraft returning to bases in western Europe.

41.
Omega Navigation System
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OMEGA was the first truly global-range radio navigation system, operated by the United States in cooperation with six partner nations. It became operational around 1971 and was shut down in 1997 in favour of the Global Positioning Satellite system, taking a fix in any navigation system requires the determination of two measurements. Typically these are taken in relation to fixed objects like prominent landmarks or the location of radio transmission towers. By measuring the angle to two locations, the position of the navigator can be determined. Alternately, one can measure the angle and distance to a single object, the introduction of radio systems during the 20th century dramatically increased the distances over which measurements could be taken. A variety of methods were developed to take fixes with relatively small angle inaccuracies, the same electronics that made basic radio systems work introduced the possibility of making very accurate time delay measurements. This enabled accurate measurement of the delay between the transmission and reception of the signal, the delay measurement could be used to determine the distance between the two transmitters. The problem was knowing when the transmission was initiated, with radar, this was simple, as the transmitter and receiver were usually at the same location. Measuring the delay between sending the signal and receiving the echo allowed accurate range measurement, for other uses, air navigation for instance, the receiver would have to know the precise time the signal was transmitted. This was not generally possible using electronics of the day, instead, two stations were synchronized by using one of the two transmitted signals as the trigger for the second signal. By comparing the measured delay between the two signals, and comparing that with the delay, the aircrafts position was revealed to lie along a curved line in space. By making two such measurements against widely separated stations, the lines would overlap in two locations. These locations were normally far enough apart to allow conventional navigation systems, like dead reckoning, the first of these hyperbolic navigation systems was the UKS Gee and Decca, followed by the US LORAN and LORAN-C systems. LORAN-C offered accurate navigation at distances over 1,000 kilometres, key to the operation of the hyperbolic system was the use of one transmitter to broadcast the master signal, which was used by the secondaries as their trigger. This limited the range over which the system could operate. For very short ranges, tens of kilometres, the signal could be carried by wires. Over long distances, over-the-air signalling was more practical, but all such systems had range limits of one sort or another, very long distance radio signalling is possible, using longwave techniques, which enables a planet-wide hyperbolic system. However, at those ranges, radio signals do not travel in straight lines, at medium frequencies, this appears to bend or refract the signal beyond the horizon

Omega Navigation System
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The Communications Control Link building of the Naval Radio Station at Haiku, part of the Kaneohe Omega Transmitter, 1987
Omega Navigation System
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based on NASA Worldwind-globe [1] - location of Omega-transmitter A in Norway (distances)
Omega Navigation System
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Omega Tower Paynesville, Liberia
Omega Navigation System
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Person abseiling down the former VLF Transmitter Woodside Station G OMEGA transmitter in Woodside, Victoria.

42.
Longwave
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In radio, longwave, also written as long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an one, dating from the early 20th century, when the radio spectrum was considered to consist of long, medium. Most modern radio systems and devices use wavelengths which would then have been considered ultra-short, in contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Sometimes, part of the frequency band is included. The International Telecommunication Union Region 1 longwave broadcast band falls wholly within the low band of the radio spectrum. Broader definitions of longwave may extend below and/or above it, in the US, the Longwave Club of America is interested in frequencies below the AM broadcast band, i. e. all frequencies below 535 kHz. Because of their wavelength, radio waves in this frequency range can diffract over obstacles like mountain ranges and travel beyond the horizon. This mode of propagation, called ground wave, is the mode in the longwave band. The attenuation of signal strength with distance by absorption in the ground is lower than at higher frequencies, Low frequency ground waves can be received up to 2,000 kilometres from the transmitting antenna. Low frequency waves can also travel long distances by reflecting from the ionosphere, although this method. Reflection occurs at the ionospheric E layer or F layers, skywave signals can be detected at distances exceeding 300 kilometres from the transmitting antenna. Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and they identify themselves by a callsign in Morse code. They can occupy any frequency in the range 190–1750 kHz, in North America, they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz, there are government broadcast stations in the range 40–80 kHz that transmit coded time signals to radio clocks. Radio controlled clocks receive their time calibration signals with built-in long-wave receivers, long-waves travel by groundwaves that hug the surface of the earth, unlike medium-waves and short-waves. Those higher-frequency signals do not follow the surface of the Earth beyond a few kilometers and these different propagation paths can make the time lag different for every signal received. The military of the United Kingdom, Russian Federation, United States, Germany, in North America during the 1970s, the frequencies 167,179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays, in the United States, Part 15 of FCC regulations allow unlicensed use of 136 kHz and this is called Low Frequency Experimental Radio

Longwave
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The tuning dial on a 1940s radio, showing longwave wavelengths between 800 and 2000 metres, corresponding to frequencies between 375 and 150 kHz

43.
Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s

Transmitter
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Continental 816R-5B 35 kW FM transmitter, belonging to American FM radio station KWNR broadcasting on 95.5 MHz in Las Vegas
Transmitter
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Commercial FM broadcasting transmitter at radio station WDET-FM, Wayne State University, Detroit, USA. It broadcasts at 101.9 MHz with a radiated power of 48 kW.
Transmitter
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Modern amateur radio transceiver, the ICOM IC-746PRO. It can transmit on the amateur bands from 1.8 MHz to 144 MHz with an output power of 100 W
Transmitter
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A CB radiotransceiver, a two way radio transmitting on 27 MHz with a power of 4 W, that can be operated without a license

44.
Fix (position)
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In position fixing navigation, a position fix or simply a fix is a position derived from measuring external reference points. A visual fix can be made by using any sighting device with a bearing indicator, two or more objects of known position are sighted, and the bearings recorded. Bearing lines are plotted on a chart through the locations of the sighted items. The intersection of lines is then the current position of the vessel. Usually, a fix is where two or more position lines intersect at any given time. If three position lines can be obtained, the cocked hat, where the 3 lines do not intersect at the same point. The most accurate fixes occur when the lines are at right angles to each other. Fixes are a part of navigation by dead reckoning because dead reckoning relies on estimates of speed. The fix confirms the position during a journey. The fix itself can introduce inaccuracies if the point is not correctly identified or is inaccurately measured

Fix (position)
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Visual fix by three bearings plotted on a nautical chart

45.
Transit (satellite)
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The Transit system, also known as NAVSAT or NNSS, was the first satellite navigation system to be used operationally. The system was used by the U. S. Transit provided continuous navigation satellite service from 1964, initially for Polaris submarines and they were able to determine Sputniks orbit by analyzing the Doppler shift of its radio signals during a single pass. Development of the Transit system began in 1958, and a prototype satellite and that satellite failed to reach orbit. A second satellite, Transit 1B, was successfully launched April 13,1960, the first successful tests of the system were made in 1960, and the system entered Naval service in 1964. The Chance Vought/LTV Scout rocket was selected as the launch vehicle for the program because it delivered a payload into orbit for the lowest cost per pound. However, the Scout decision imposed two design constraints, first, the weight of the earlier satellites was about 300 lb each, but the Scout launch capacity to the Transit orbit was about 120 lb. A satellite mass reduction had to be achieved, despite a demand for power than APL had previously designed into a satellite. The second problem concerned the increased vibration that affected the payload during launching because the Scout used solid rocket motors, thus, electronic equipment that was smaller than before and rugged enough to withstand the increased vibration of launch had to be produced. Meeting the new demands was more difficult than expected, but it was accomplished, the first prototype operational satellite was launched into a polar orbit by a Scout rocket on 18 December 1962. The satellite verified a new technique for deploying the solar panels and for separating from the rocket, Transit 5A-2, launched on 5 April 1963, failed to achieve orbit. Transit 5A-3, with a power supply, was launched on 15 June 1963. A malfunction of the memory occurred during powered flight that kept it from accepting and storing the navigation message, thus, 5A-3 could not be used for navigation. However, this satellite was the first to achieve gravity-gradient stabilization, surveyors used Transit to locate remote benchmarks by averaging dozens of Transit fixes, producing sub-meter accuracy. In fact, the elevation of Mount Everest was corrected in the late 1980s by using a Transit receiver to re-survey a nearby benchmark, thousands of warships, freighters and private watercraft used Transit from 1967 until 1991. In the 1970s, the Soviet Union started launching their own navigation system Parus / Tsikada. Some Soviet warships were equipped with Motorola NavSat receivers, the Transit system was made obsolete by the Global Positioning System, and ceased navigation service in 1996. Improvements in electronics allowed GPS receivers to effectively take several fixes at once, GPS uses many more satellites than were used with Transit, allowing the system to be used continuously, while Transit provided a fix only every hour or more

46.
Doppler effect
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The Doppler effect is the change in frequency or wavelength of a wave for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, a common example of Doppler shift is the change of pitch heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the frequency, the received frequency is higher during the approach, identical at the instant of passing by. When the source of the waves is moving towards the observer, therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency, while they are travelling, the distance between successive wave fronts is reduced, so the waves bunch together. The distance between wave fronts is then increased, so the waves spread out. For waves that propagate in a medium, such as sound waves, the total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately, for waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered. Doppler first proposed this effect in 1842 in his treatise Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels, the hypothesis was tested for sound waves by Buys Ballot in 1845. He confirmed that the pitch was higher than the emitted frequency when the sound source approached him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848, in Britain, John Scott Russell made an experimental study of the Doppler effect. The frequency is decreased if either is moving away from the other, the above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle, the frequency that is first heard is higher than the objects emitted frequency. When the observer is close to the path of the object. When the observer is far from the path of the object, to understand what happens, consider the following analogy. Someone throws one ball every second at a man, assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be spaced out

47.
US Naval Observatory
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The USNO operates the Master Clock, which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, aside from its scientific mission, a house located within the Naval Observatory complex serves as the official residence of the Vice President of the United States. President John Quincy Adams, who in 1825 signed the bill for the creation of an observatory just before leaving presidential office, had intended for it to be called the National Observatory. The names National Observatory and Naval Observatory were both used for 10 years, until a ruling was passed to use the latter. Adams had made protracted efforts to bring astronomy to a level at that time. He spent many nights at the observatory, watching and charting the stars, established by the order of the United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments, the Observatory rose from humble beginnings. Placed under the command of Lieutenant Louis M. Goldsborough, with an budget of $330, its primary function was the restoration, repair. It was made into an observatory in 1842 via a federal law. Lieutenant James Melville Gilliss was put in charge of obtaining the instruments needed, lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and scientific devices and books. The observatorys primary mission was to care for the United States Navys marine chronometers, charts and it calibrated ships chronometers by timing the transit of stars across the meridian. These facilities were listed on the National Register of Historic Places in 2017, the first superintendent was Navy Commander Matthew Fontaine Maury. Maury had the worlds first vulcanized time ball, created to his specifications by Charles Goodyear for the U. S. Observatory and it was the first time ball in the United States, being placed into service in 1845, and the 12th in the world. Maury kept accurate time by the stars and planets, the time ball was dropped every day except Sunday precisely at the astronomically defined moment of Mean Solar Noon, enabling all ships and civilians to know the exact time. Time was also sold to the railroads and was used in conjunction with railroad chronometers to schedule American rail transport, early in the 20th century, the Arlington Time Signal broadcast this service to wireless receivers. In 1849 the Nautical Almanac Office was established in Cambridge, Massachusetts as a separate organization and it was moved to Washington, D. C. in 1866, colocating with the U. S. Naval Observatory in 1893. On September 20,1894, the NAO became a branch of USNO, the astronomical measurements taken of the transit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of the AU. Relying heavily on methods, the naval observers returned 350 photographic plates in 1874. This calculated distance was a significant improvement over several previous estimates, the telescope used for the discovery of the Moons of Mars was the 26-inch refractor, then located at Foggy Bottom

US Naval Observatory
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Aerial view of the U.S. Naval Observatory
US Naval Observatory
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The Seal of the USNO with a quote from the Astronomicon, Adde gubernandi studium: Pervenit in astra, et pontum caelo conjunxit, "Increase the study of navigation: it arrives in the stars, and marries the sea with heaven"
US Naval Observatory
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Naval Observatory Flagstaff Station in Operation
US Naval Observatory
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Number One Observatory Circle, official home of the Vice President of the United States

48.
Ephemeris
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In astronomy and celestial navigation, an ephemeris gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times. Historically, positions were given as printed tables of values, given at intervals of date. Modern ephemerides are often computed electronically from mathematical models of the motion of astronomical objects, the astronomical position calculated from an ephemeris is given in the spherical polar coordinate system of right ascension and declination. Ephemerides are used in navigation and astronomy. They are also used by some astrologers, 1st millennium BC — Ephemerides in Babylonian astronomy. 13th century — the Zīj-i Īlkhānī were compiled at the Maragheh observatory in Persia, 13th century — the Alfonsine Tables were compiled in Spain to correct anomalies in the Tables of Toledo, remaining the standard European ephemeris until the Prutenic Tables almost 300 years later. 1531 — Work of Johannes Stöffler is published posthumously at Tübingen,1551 — the Prutenic Tables of Erasmus Reinhold were published, based on Copernicuss theories. 1554 — Johannes Stadius published Ephemerides novae et auctae, the first major ephemeris computed according to Copernicus heliocentric model, one of the users of Stadiuss tables is Tycho Brahe. 1627 — the Rudolphine Tables of Johannes Kepler based on elliptical planetary motion became the new standard. 1679 — La Connaissance des Temps ou calendrier et éphémérides du lever & coucher du Soleil, de la Lune & des autres planètes, first published yearly by Jean Picard and still extent. According to Gingerich, the patterns are as distinctive as fingerprints. Typically, such ephemerides cover several centuries, past and future, nevertheless, there are secular phenomena which cannot adequately be considered by ephemerides. The greatest uncertainties in the positions of planets are caused by the perturbations of asteroids, most of whose masses and orbits are poorly known. Reflecting the continuing influx of new data and observations, NASAs Jet Propulsion Laboratory has revised its published ephemerides nearly every year for the past 20 years. Solar system ephemerides are essential for the navigation of spacecraft and for all kinds of observations of the planets, their natural satellites, stars. The equinox of the system must be given. It is, in all cases, either the actual equinox, or that of one of the standard equinoxes, typically J2000.0, B1950.0. Star maps almost always use one of the standard equinoxes, Ephemerides of the planet Saturn also sometimes contain the apparent inclination of its ring

49.
Atomic clock
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The principle of operation of an atomic clock is not based on nuclear physics, but rather on atomic physics, it uses the microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were based on masers at room temperature, currently, the most accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, one of the primary time. The accuracy of an atomic clock depends on two factors, the first factor is temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times. The second factor is the frequency and intrinsic width of the electronic transition, higher frequencies and narrow lines increase the precision. National standards agencies in many countries maintain a network of atomic clocks which are intercompared and these clocks collectively define a continuous and stable time scale, International Atomic Time. For civil time, another time scale is disseminated, Coordinated Universal Time, UTC is derived from TAI, but approximately synchronised, by using leap seconds, to UT1, which is based on actual rotation of the Earth with respect to the solar time. The idea of using atomic transitions to measure time was suggested by Lord Kelvin in 1879, magnetic resonance, developed in the 1930s by Isidor Rabi, became the practical method for doing this. In 1945, Rabi first publicly suggested that atomic beam magnetic resonance might be used as the basis of a clock, the first atomic clock was an ammonia maser device built in 1949 at the U. S. National Bureau of Standards. It was less accurate than existing quartz clocks, but served to demonstrate the concept, calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time. This led to the agreed definition of the latest SI second being based on atomic time. Equality of the ET second with the SI second has been verified to within 1 part in 1010, the SI second thus inherits the effect of decisions by the original designers of the ephemeris time scale, determining the length of the ET second. Since the beginning of development in the 1950s, atomic clocks have been based on the transitions in hydrogen-1, caesium-133. The first commercial atomic clock was the Atomichron, manufactured by the National Company, more than 50 were sold between 1956 and 1960. This bulky and expensive instrument was replaced by much smaller rack-mountable devices, such as the Hewlett-Packard model 5060 caesium frequency standard. In August 2004, NIST scientists demonstrated a chip-scale atomic clock, according to the researchers, the clock was believed to be one-hundredth the size of any other. It requires no more than 125 mW, making it suitable for battery-driven applications and this technology became available commercially in 2011. Ion trap experimental optical clocks are more precise than the current caesium standard, in March 2017, NASA plans to deploy the Deep Space Atomic Clock, a miniaturized, ultra-precise mercury-ion atomic clock, into outer space

Atomic clock
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FOCS 1, a continuous cold caesium fountain atomic clock in Switzerland, started operating in 2004 at an uncertainty of one second in 30 million years.
Atomic clock
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The master atomic clock ensemble at the U.S. Naval Observatory in Washington, D.C., which provides the time standard for the U.S. Department of Defense. The rack mounted units in the background are Symmetricom (formerly HP) 5071A caesium beam clocks. The black units in the foreground are Symmetricom (formerly Sigma-Tau) MHM-2010 hydrogen maser standards.
Atomic clock
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Louis Essen (right) and Jack Parry (left) standing next to the world's first caesium-133 atomic clock.
Atomic clock
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Chip-scale atomic clocks, such as this one unveiled in 2004, are expected to greatly improve GPS location.

50.
Beidou Navigation Satellite System
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The BeiDou Navigation Satellite System is a Chinese satellite navigation system. It consists of two separate satellite constellations – a limited test system that has been operating since 2000, the first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites and offers limited coverage and applications. It has been offering services, mainly for customers in China and neighboring regions. It became operational in China in December 2011, with 10 satellites in use and it is planned to begin serving global customers upon its completion in 2020. In-mid 2015, China started the build-up of the third generation BeiDou system in the global coverage constellation, the first BDS-3 satellite was launched 30 September 2015. As of March 2016,4 BDS-3 in-orbit validation satellites have been launched, the official English name of the system is BeiDou Navigation Satellite System. It is named after the Big Dipper constellation, which is known in Chinese as Běidǒu, the name literally means Northern Dipper, the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris, as such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system. The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun, the third satellite, BeiDou-1C, was put into orbit on 25 May 2003. The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system. On 2 November 2006, China announced that from 2008 BeiDou would offer a service with an accuracy of 10 meters, timing of 0.2 microseconds. In February 2007, the fourth and last satellite of the BeiDou-1 system and it was reported that the satellite had suffered from a control system malfunction but was then fully restored. In April 2007, the first satellite of BeiDou-2, namely Compass-M1 was successfully put into its working orbit, the second BeiDou-2 constellation satellite Compass-G2 was launched on 15 April 2009. On 2 June 2010, the satellite was launched successfully into orbit. The fifth orbiter was launched into space from Xichang Satellite Launch Center by an LM-3I carrier rocket on 1 August 2010, three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C. Another satellite, the Beidou-2/Compass IGSO-5 satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011. In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million in Galileo over the few years. At the time, it was believed that Chinas BeiDou navigation system would only be used by its armed forces

Beidou Navigation Satellite System
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The BeiDou system's logo
Beidou Navigation Satellite System
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Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.
Beidou Navigation Satellite System
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Ground track of BeiDou-M5 (2012-050A)